There are several potential challenges associated with routine screening for HCM in the United States. First, the U.S. athlete population of 15 million is almost twice as large as Italy's estimated athlete population. Second, these events are rare, with fewer than 100 deaths in the U.S. due to HCM in competitive athletes per year, or about 1 death per 220,000 athletes. Lastly, genetic testing would provide a definitive diagnosis; however, due to the numerous HCM-causing mutations, this method of screening is complex and is not cost-effective. Therefore, genetic testing in the United States is limited to individuals who exhibit clear symptoms of HCM, and their family members. This ensures that the test is not wasted on detecting other causes of ventricular hypertrophy (due to its low sensitivity), and that family members of the individual are educated on the potential risk of being carriers of the mutant gene(s).

Canadian genetic testing guidelines and recommendations for individuals diagnosed with HCM are as follows:

- The main purpose of genetic testing is for screening family members.

- According to the results, at-risk relatives may be encouraged to undergo extensive testing.

- Genetic testing is not meant for confirming a diagnosis.

- If the diagnosed individual has no relatives that are at risk, then genetic testing is not required.

- Genetic testing is not intended for risk assessment or treatment decisions.

- Evidence only supports clinical testing in predicting the progression and risk of developing complications of HCM.

For individuals "suspected" of having HCM:

- Genetic testing is not recommended for determining other causes of left ventricular hypertrophy (such as "athlete's heart", hypertension, and cardiac amyloidosis).

- HCM may be differentiated from other hypertrophy-causing conditions using clinical history and clinical testing.

Although the disease is more common in African-Americans than in Caucasians, it may occur in any patient population.

Although in many cases no cause is apparent, dilated cardiomyopathy is probably the result of damage to the myocardium produced by a variety of toxic, metabolic, or infectious agents. It may be due to fibrous change of the myocardium from a previous myocardial infarction. Or, it may be the late sequelae of acute viral myocarditis, such as with Coxsackie B virus and other enteroviruses possibly mediated through an immunologic mechanism.

Other causes include:

- Chagas disease, due to "Trypanosoma cruzi". This is the most common infectious cause of dilated cardiomyopathy in Latin America

- Pregnancy. Dilated cardiomyopathy occurs late in gestation or several weeks to months postpartum as a peripartum cardiomyopathy. It is reversible in half of cases.

- Alcohol abuse (alcoholic cardiomyopathy)

- Nonalcoholic toxic insults include administration of certain chemotherapeutic agents, in particular doxorubicin (Adriamycin), and cobalt.

- Thyroid disease

- Inflammatory diseases such as sarcoidosis and connective tissue diseases

- Tachycardia-induced cardiomyopathy

- Muscular dystrophy

- Tuberculosis - 1 to 2% of TB cases.

- Autoimmune mechanisms

Recent studies have shown that those subjects with an extremely high occurrence (several thousands a day) of premature ventricular contractions (extrasystole) can develop dilated cardiomyopathy. In these cases, if the extrasystole are reduced or removed (for example, via ablation therapy) the cardiomyopathy usually regresses.

Due to non-compaction cardiomyopathy being a relatively new disease, its impact on human life expectancy is not very well understood. In a 2005 study that documented the long-term follow-up of 34 patients with NCC, 35% had died at the age of 42 +/- 40 months, with a further 12% having to undergo a heart transplant due to heart failure. However, this study was based upon symptomatic patients referred to a tertiary-care center, and so were suffering from more severe forms of NCC than might be found typically in the population. Sedaghat-Hamedani et al. also showed the clinical course of symptomatic LVNC can be severe. In this study cardiovascular events were significantly more frequent in LVNC patients compared with an age-matched group of patients with non-ischaemic dilated cardiomyopathy (DCM). As NCC is a genetic disease, immediate family members are being tested as a precaution, which is turning up more supposedly healthy people with NCC who are asymptomatic. The long-term prognosis for these people is currently unknown.

Cardiomyopathies are either confined to the heart or are part of a generalized systemic disorder, both often leading to cardiovascular death or progressive heart failure-related disability. Other diseases that cause heart muscle dysfunction are excluded, such as coronary artery disease, hypertension, or abnormalities of the heart valves. Often, the underlying cause remains unknown, but in many cases the cause may identifiable. Alcoholism, for example, has been identified as a cause of dilated cardiomyopathy, as has drug toxicity, and certain infections (including Hepatitis C). On the other hand, molecular biology and genetics have given rise to the recognition of various genetic causes. For example, mutations in the cardiac desmosomal genes as well as in the DES gene may cause arrhythmogenic right ventricular cardiomyopathy (ARVC).

A more clinical categorization of cardiomyopathy as 'hypertrophied', 'dilated', or 'restrictive', has become difficult to maintain because some of the conditions could fulfill more than one of those three categories at any particular stage of their development. The current American Heart Association definition divides cardiomyopathies into primary, which affect the heart alone, and secondary, which are the result of illness affecting other parts of the body. These categories are further broken down into subgroups which incorporate new genetic and molecular biology knowledge.

The cause of cardiomegaly is not well understood and many cases of cardiomegaly are idiopathic (having no known cause). Prevention of cardiomegaly starts with detection. If a person has a family history of cardiomegaly, one should let one's doctor know so that treatments can be implemented to help prevent worsening of the condition. In addition, prevention includes avoiding certain lifestyle risk factors such as tobacco use and controlling one's high cholesterol, high blood pressure, and diabetes. Non-lifestyle risk factors include family history of cardiomegaly, coronary artery disease (CAD), congenital heart failure, Atherosclerotic disease, valvular heart disease, exposure to cardiac toxins, sleep disordered breathing (such as sleep apnea), sustained cardiac arrhythmias, abnormal electrocardiograms, and cardiomegaly on chest X-ray. Lifestyle factors which can help prevent cardiomegaly include eating a healthy diet, controlling blood pressure, exercise, medications, and not abusing alcohol and cocaine. Current research and the evidence of previous cases link the following (below) as possible causes of cardiomegaly.

The most common causes of Cardiomegaly are congenital (patients are born with the condition based on a genetic inheritance), high blood pressure which can enlarge the left ventricle causing the heart muscle to weaken over time, and coronary artery disease that creates blockages in the heart's blood supply, which can bring on a cardiac infarction (heart attack) leading to tissue death which causes other areas of the heart to work harder, increasing the heart size.

Other possible causes include:

- Heart Valve Disease

- Cardiomyopathy (disease to the heart muscle)

- Pulmonary Hypertension

- Pericardial Effusion (fluid around the heart)

- Thyroid Disorders

- Hemochromatosis (excessive iron in the blood)

- Other rare diseases like Amyloidosis

- Viral infection of the heart

- Pregnancy, with enlarged heart developing around the time of delivery (peripartum cardiomyopathy)

- Kidney disease requiring dialysis

- Alcohol or cocaine abuse

- HIV infection

- Diabetes

Endomyocardial fibrosis is generally limited to the tropics and sub-saharan Africa. The highest incidence of death caused by cardiac sarcoidosis is found in Japan.

Symptoms of cardiomyopathies may include fatigue, swelling of the lower extremities and shortness of breath. Further indications of the condtion may include:

- Arrhythmia

- Fainting

- Diziness

HIV is a major cause of cardiomyopathy – in particular dilated cardiomyopathy. Dilated cardiomyopathy can be due to pericardial effusion or infective endocarditis, especially in intravenous drug users which are common in the HIV population. However, the most researched causes of cardiomyopathy are myocardial inflammation and infection caused by HIV-1. Toxoplasma gondii is the most common opportunistic infectious agent associated with myocarditis in AIDS. Coinfection with viruses (usually, coxsackievirus B3 and cytomegalovirus) seems to have an important affect in myocarditis. HIV-1 infection produces additional virus and cytokines such as TNF-α. This induces cardiomyocyte apoptosis. TNF-α causes a negative inotropic effect by interfering with the intracellular calcium ion concentrations. The intensity of the stains for TNF-α and iNOS of the myocardium was greater in patients with HIV associated cardiomyopathy, myocardial viral infection and was inversely correlated with CD4 count with antiretroviral therapy having no effect. Cardiac autoimmunity affects the pathogenesis of HIV-related heart disease as HIV-infected patients with dilated cardiomyopathy are more likely to have cardiac-specific autoantibodies than HIV-infected patients with healthy hearts and HIV-negative controls. Many patients with HIV have nutritional deficiencies which have been linked to left ventricular dysfunction. HIV-infected patients with encephalopathy are more likely to die of congestive heart failure than are those without encephalopathy. HAART has reduced the incidence of myocarditis thus reducing the prevalence of HIV-associated cardiomyopathy. Intravenous immunoglobulins (IVIGs) can also help patients with HIV-associated myocarditis.

Due to its recent establishment as a diagnosis, and it being unclassified as a cardiomyopathy according to the WHO, it is not fully understood how common the condition is. Some reports suggest that it is in the order of 0.12 cases per 100,000. The low number of reported cases though is due to the lack of any large population studies into the disease and have been based primarily upon patients suffering from advanced heart failure. A similar situation occurred with hypertrophic cardiomyopathy, which was initially considered very rare; however is now thought to occur in one in every 500 people in the population.

Again due to this condition being established as a diagnosis recently, there are ongoing discussions as to its nature, and to various points such as the ratio of compacted to non-compacted at different age stages. However it is universally understood that non-compaction cardiomyopathy will be characterized anatomically by "deep trabeculations in the ventricular wall, which define recesses communicating with the main ventricular chamber. Major clinical correlates include systolic and diastolic dysfunction, associated at times with systemic embolic events."

Signs and symptoms such as malabsorption and diarrhoea respectively, may occur with HIV infection causing many HIV patients to have nutritional deficiencies and altered levels of vitamin B12, carnitine, and growth and thyroid hormones - all have been associated with left ventricular dysfunction. A lowered BMI in HIV patients is also associated with cardiomyopathy.

Boxer cardiomyopathy is a genetic disease inherited in an autosomal dominant pattern. The presentation in affected offspring is quite variable, suggesting incomplete penetrance. In 2009, a group led by Dr. Kathryn Meurs at Washington State University announced that they had identified one genetic anomaly associated with Boxer cardiomyopathy but as of 2012 there is still debate over the significance of the discovery.

RCM can be caused by genetic or non-genetic factors. Thus it is possible to divide the causes into primary and secondary. The common modern organization is into "Infiltrative", "storage diseases", "non-infiltrative", and "endomyocardial" etiologies:

The most common cause of restrictive cardiomyopathy is amyloidosis.

All dogs with Boxer cardiomyopathy are at risk of sudden cardiac death. This includes asymptomatic dogs, meaning that sudden death may be the first sign of disease.

Sudden cardiac death is usually caused by the degeneration of ventricular tachycardia to ventricular fibrillation. Unless terminated promptly by defibrillation, death usually occurs within minutes.

Treatment for alcoholic cardiomyopathy involves lifestyle changes, including complete abstinence from alcohol use, a low sodium diet, and fluid restriction, as well as medications. Medications may include ACE inhibitors, beta blockers, and diuretics which are commonly used in other forms of cardiomyopathy to reduce the strain on the heart. Persons with congestive heart failure may be considered for surgical insertion of an ICD or a pacemaker which can improve heart function. In cases where the heart failure is irreversible and worsening, heart transplant may be considered.

Treatment will possibly prevent the heart from further deterioration, and the cardiomyopathy is largely reversible if complete abstinence from alcohol is maintained.

Any condition or process that leads to stiffening of the left ventricle can lead to diastolic dysfunction. Causes of left ventricular stiffening include:

- A long-standing hypertension where, as a result of left ventricular muscle hypertrophy caused by the high pressure, the left ventricle has become stiff.

- Aortic stenosis of any cause where the ventricular muscle becomes hypertrophied, and thence stiff, as a result of the increased pressure load placed on it by the stenosis.

- Diabetes

- Age – elderly patients mainly if they have hypertension.

Causes of isolated right ventricular diastolic failure are uncommon. These causes include:

- Constrictive pericarditis

- Restrictive cardiomyopathy, which includes Amyloidosis (most common restrictive), Sarcoidosis and fibrosis.

The true incidence of TIC is unclear. Some studies have noted the incidence of TIC in adults with irregular heart rhythms to range from 8% to 34%. Other studies of patients with atrial fibrillation and left ventricular dysfunction estimate that 25-50% of these study participants have some degree of TIC. TIC has been reported in all age groups.

Treatments for cardiomegaly include a combination of medication treatment and medical/surgical procedures. Below are some of the treatment options for individuals with cardiomegaly:

Medications

- Diuretics: to lower the amount of sodium and water in the body, which can help lower the pressure in the arteries and heart.

- Angiotensin-converting enzyme (ACE) inhibitors: to lower the blood pressure and improve the heart's pumping ability.

- Angiotensin receptor blockers (ARBs): to provide the benefits of ACE inhibitors for those who can't take ACE inhibitors.

- Beta blockers: to lower blood pressure and improve heart function.

- Digoxin: to help improve the pumping function of the heart and lessen the need for hospitalization for heart failure.

- Anticoagulants: to reduce the risk of blood clots that could cause a heart attack or stroke.

- Anti-arrhythmics: to keep the heart beating with a normal rhythm.

Medical devices to regulate the heartbeat

- Pacemaker: Coordinates the contractions between the left and right ventricle. In people who may be at risk of serious arrhythmias, drug therapy or an implantable cardioverter-defibrillator (ICD) may be used.

- ICDs: Small devices implanted in the chest to constantly monitor the heart rhythm and deliver electrical shocks when needed to control abnormal, rapid heartbeats. The devices can also work as pacemakers.

Surgical procedures

- Heart valve surgery: If an enlarged heart is caused by a problem with one of the heart valves, one may have surgery to remove the valve and replace it with either an artificial valve or a tissue valve from a pig, cow or deceased human donor. If blood leaks backward through a valve (valve regurgitation), the leaky valve may be surgically repaired or replaced.

- Coronary bypass surgery: If an enlarged heart is related to coronary artery disease, one may opt to have coronary artery bypass surgery.

- Left ventricular assist device: (LVAD): This implantable mechanical pump helps a weak heart pump. LVADs are often implanted while a patient waits for a heart transplant or, if the patient is not a heart transplant candidate, as a long-term treatment for heart failure.

- Heart transplant: If medications can't control the symptoms, a heart transplant is often a final option.

Cardiomegaly can progress and certain complications are common:

- Heart failure: One of the most serious types of enlarged heart, an enlarged left ventricle, increases the risk of heart failure. In heart failure, the heart muscle weakens, and the ventricles stretch (dilate) to the point that the heart can't pump blood efficiently throughout the body.

- Blood clots: Having an enlarged heart may make one more susceptible to forming blood clots in the lining of the heart. If clots enter the bloodstream, they can block blood flow to vital organs, even causing a heart attack or stroke. Clots that develop on the right side of the heart may travel to the lungs, a dangerous condition called a pulmonary embolism.

- Heart murmur: For people who have an enlarged heart, two of the heart's four valves — the mitral and tricuspid valves — may not close properly because they become dilated, leading to a backflow of blood. This flow creates sounds called heart murmurs.

- NOTE* The exact mortality rate for people with cardiomegaly is unknown. However, many people live for a very long time with an enlarged heart and if detected early, treatment can help improve the condition and prolong the lives of these people.

Although not based on a human clinical trial, the only currently accepted disease-modifying therapeutic strategy available for familial amyloid cardiomyopathy is a combined liver and heart transplant. Treatments aimed at symptom relief are available, and include diuretics, pacemakers, and arrhythmia management. Thus, Senile systemic amyloidosis and familial amyloid polyneuropathy are often treatable diseases that are misdiagnosed.

In 2013, the European Medicines Agency approved the drug tafamidis (Vyndaqel) to slow the progression of familial amyloid polyneuropathy, a related disease caused by TTR aggregation that first presents as an autonomic and/or peripheral neuropathy (later progressing to a cardiomyopathy).

Takotsubo cardiomyopathy is rare, affecting between 1.2% and 2.2% of people in Japan and 2% to 3% in western countries who suffer a myocardial infarction. It also affects far more women than men with 90% of cases being women, most postmenopausal. Scientists believe one reason is that estrogen causes the release of catecholamine and glucocorticoid in response to mental stress. It is not likely for the same recovered patient to experience the syndrome twice, although it has happened in rare cases. The average ages at onset are between 58 and 75 years. Less than 3% of cases occurred in patients under age 50.

As an overall medical condition PVCs are normally not very harmful to patients that experience them, but frequent PVCs may put patients at increased risk of developing arrhythmias or cardiomyopathy, which can greatly impact the functioning of the heart over the span of that patient's life. On a more serious and severe scale, frequent PVCs can accompany underlying heart disease and lead to chaotic, dangerous heart rhythms and possibly sudden cardiac death.

Asymptomatic patients that do not have heart disease have long-term prognoses very similar to the general population, but asymptomatic patients that have ejection fractions greater than 40% have a 3.5% incidence of sustained ventricular tachycardia or cardiac arrest. One drawback comes from emerging data that suggests very frequent ventricular ectopy may be associated with cardiomyopathy through a mechanism thought to be similar to that of chronic right ventricular pacing associated cardiomyopathy. Patients that have underlying chronic structural heart disease and complex ectopy, mortality is significantly increased.

In meta-analysis of 11 studies, people with frequent PVC (≥1 time during a standard electrocardiographic recording or ≥30 times over a 1-hour recording) had risk of cardiac death 2 times higher than persons without frequent PVC. Although most studies made attempts to exclude high-risk subjects, such as those with histories of cardiovascular disease, they did not test participants for underlying structural heart disease.

In a study of 239 people with frequent PVCs (>1000 beats/day) and without structural heart disease (i.e. in the presence of normal heart function) there were no serious cardiac events through 5.6 years on average, but there was correlation between PVC prevalence and decrease of ejection fraction and increase of left ventricular diastolic dimension. In this study absence of heart of disease was excluded by echocardiography, cardiac magnetic resonance imaging in 63 persons and Holter monitoring.

Another study has suggested that in the absence of structural heart disease even frequent (> 60/h or 1/min) and complex PVCs are associated with a benign prognosis. It was study of 70 people followed by 6.5 years on average. Healthy status was confirmed by extensive noninvasive cardiologic examination, although cardiac catheterization of a subgroup disclosed serious coronary artery disease in 19%. Overall survival was better than expected.

On the other hand, the Framingham Heart Study reported that PVCs in apparently healthy people were associated with a twofold increase in the risk of all-cause mortality, myocardial infarction and cardiac death. In men with coronary heart disease and in women with or without coronary heart disease, complex or frequent arrhythmias were not associated with an increased risk. The at-risk people might have subclinical coronary disease. These Framingham results have been criticised for the lack of rigorous measures to exclude the potential confounder of underlying heart disease.

In the ARIC study of 14,783 people followed for 15 to 17 years those with detected PVC during 2 minute ECG, and without hypertension or diabetes on the beginning, had risk of stroke increased by 109%. Hypertension or diabetes, both risk factors for stroke, did not change significantly risk of stroke for people with PVC. It is possible that PVCs identified those at risk of stroke with blood pressure and impaired glucose tolerance on a continuum of risk below conventional diagnostic thresholds for hypertension and diabetes. Those in ARIC study with any PVC had risk of heart failure increased by 63% and were >2 times as likely to die due to coronary heart disease (CHD). Risk was also higher for people with or without baseline CHD.

In the Niigata study of 63,386 people with 10-year follow-up period those with PVC during a 10-second recording had risk of atrial fibrillation increased nearly 3 times independently from risk factors: age, male sex, body mass index, hypertension, systolic and diastolic blood pressure, and diabetes.

Reducing frequent PVC (>20%) by antiarrhythmic drugs or by catheter ablation significantly improves heart performance.

Recent studies have shown that those subjects who have an extremely high occurrence of PVCs (several thousand a day) can develop dilated cardiomyopathy. In these cases, if the PVCs are reduced or removed (for example, via ablation therapy) the cardiomyopathy usually regresses.

Also, PVCs can permanently cease without any treatment, in a material percentage of cases.

The cause of takotsubo cardiomyopathy is not fully understood, but several mechanisms have been proposed.

1. Transient vasospasm: Some of the original researchers of takotsubo suggested that multiple simultaneous spasms of coronary arteries could cause enough loss of blood flow to cause transient stunning of the myocardium. Other researchers have shown that vasospasm is much less common than initially thought. It has been noted that when there are vasospasms, even in multiple arteries, that they do not correlate with the areas of myocardium that are not contracting.

2. Microvascular dysfunction: The theory gaining the most traction is that there is dysfunction of the coronary arteries at the level where they are no longer visible by coronary angiography. This could include microvascular vasospasm, however, it may well have some similarities to diseases such as diabetes mellitus. In such disease conditions the microvascular arteries fail to provide adequate oxygen to the myocardium.

3. Mid-ventricular obstruction, apical stunning: It has been suggested that a mid-ventricular wall thickening with outflow obstruction is important in the pathophysiology.

4. Catecholamine-induced myocyte injury: It has been suggested that the response to catecholamines (such as epinephrine and norepinephrine, released in response to stress) leads to heart muscle dysfunction that contributes to takotsubo cardiomyopathy.

It is likely that there are multiple factors at play that could including some amount of vasospasm and a failure of the microvasculature

Case series looking at large groups of patients report that some patients develop takotsubo cardiomyopathy after an emotional stress, while others have a preceding clinical stressor (such as an asthma attack or sudden illness). Roughly one-third of patients have no preceding stressful event. A 2009 large case series from Europe found that takotsubo cardiomyopathy was slightly more frequent during the winter season. This may be related to two possible/suspected pathophysiological causes: coronary spasms of microvessels, which are more prevalent in cold weather, and viral infections – such as Parvovirus B19 – which occur more frequently during the winter.

Until recently, it was generally assumed that the prognosis for individuals with diastolic dysfunction and associated intermittent pulmonary edema was better than those with systolic dysfunction. In fact, in two studies appearing in the New England Journal of Medicine in 2006, evidence was presented to suggest that the prognosis in diastolic dysfunction is the same as that in systolic dysfunction.

Molecular mechanisms underlying the coxsackievirus induced dilated cardiomyopathy is largely unknown. However, both direct viral cytotoxicity and secondary host immune responses may lead to the eventual pathogenesis.