Genetic testing for Brugada syndrome is clinically available and may help confirm a diagnosis, as well as differentiate between relatives who are at risk for the disease and those who are not. Some symptoms when pinpointing this disease include fainting, irregular heartbeats, and chaotic heartbeats. However, just detecting the irregular heartbeat may be a sign of another disease, so the doctor must detect another symptom as well.

ARVD is an autosomal dominant trait with reduced penetrance. Approximately 40–50% of ARVD patients have a mutation identified in one of several genes encoding components of the desmosome, which can help confirm a diagnosis of ARVD. Since ARVD is an autosomal dominant trait, children of an ARVD patient have a 50% chance of inheriting the disease causing mutation. Whenever a mutation is identified by genetic testing, family-specific genetic testing can be used to differentiate between relatives who are at-risk for the disease and those who are not. ARVD genetic testing is clinically available.

In some cases, the disease can be detected by observing characteristic patterns on an electrocardiogram. These patterns may be present all the time, they might be elicited by the administration of particular drugs (e.g., Class IA, such as ajmaline or procainamide, or class 1C, such as flecainide or pilsicainide, antiarrhythmic drugs that block sodium channels and cause appearance of ECG abnormalities), or they might resurface spontaneously due to as-yet unclarified triggers.

Brugada syndrome has three different ECG patterns:

- Type 1 has a coved type ST elevation with at least 2 mm (0.2 mV) J-point elevation and a gradually descending ST segment followed by a negative T-wave.

- Type 2 has a saddle-back pattern with a least 2 mm J-point elevation and at least 1 mm ST elevation with a positive or biphasic T-wave. Type 2 pattern can occasionally be seen in healthy subjects.

- Type 3 has either a coved (type 1 like) or a saddle-back (type 2 like) pattern, with less than 2 mm J-point elevation and less than 1 mm ST elevation. Type 3 pattern is not rare in healthy subjects.

The pattern seen on the ECG is persistent ST elevations in the electrocardiographic leads V-V with a right bundle branch block (RBBB) appearance, with or without the terminal S waves in the lateral leads that are associated with a typical RBBB. A prolongation of the PR interval (a conduction disturbance in the heart) is also frequently seen. The ECG can fluctuate over time, depending on the autonomic balance and the administration of antiarrhythmic drugs. Adrenergic stimulation decreases the ST segment elevation, while vagal stimulation worsens it. (There is a case report of a patient who died while shaving, presumed due to the vagal stimulation of the carotid sinus massage.)

The administration of class Ia, Ic, and III drugs increases the ST segment elevation, as does fever. Exercise decreases ST segment elevation in some people, but increases it in others (after exercise, when the body temperature has risen). The changes in heart rate induced by atrial pacing are accompanied by changes in the degree of ST segment elevation. When the heart rate decreases, the ST segment elevation increases, and when the heart rate increases, the ST segment elevation decreases. However, the contrary can also be observed.

Diagnosis depends on the clinical scenario. However, karyotyping is an essential test for diagnosis.

Transvenous biopsy of the right ventricle can be highly specific for ARVD, but it has low sensitivity. False positives include other conditions with fatty infiltration of the ventricle, such as chronic alcohol abuse and Duchenne/Becker muscular dystrophy.

False negatives are common, however, because the disease progresses typically from the epicardium to the endocardium (with the biopsy sample coming from the endocardium), and the segmental nature of the disease. Also, due to the paper-thin right ventricular free wall that is common in this disease process, most biopsy samples are taken from the ventricular septum, which is commonly "not" involved in the disease process.

A biopsy sample that is consistent with ARVD would have > 3% fat, >40% fibrous tissue, and <45% myocytes.

A post mortem histological demonstration of full thickness substitution of the RV myocardium by fatty or fibro-fatty tissue is consistent with ARVD.

If untreated, this abnormal heart rhythm can lead to dizziness, chest pain, a sensation of fluttering or pounding in the chest (palpitations), shortness of breath, or fainting (syncope). Atrial fibrillation also increases the risk of stroke. Complications of familial atrial fibrillation can occur at any age, although some people with this heart condition never experience any health problems associated with the disorder.

Atrial fibrillation is the most common type of sustained abnormal heart rhythm (arrhythmia), affecting more than 3 million people in the United States. The risk of developing this irregular heart rhythm increases with age. The incidence of the familial form of atrial fibrillation is unknown; however, recent studies suggest that up to 30 percent of all people with atrial fibrillation may have a history of the condition in their family.

Studies have shown that patients with Pacemaker syndrome and/or with sick sinus syndrome are at higher risk of developing fatal complications that calls for the patients to be carefully monitored in the ICU. Complications include atrial fibrillation, thrombo-embolic events, and heart failure.

At the time of pacemaker implantation, AV synchrony should be optimized to prevent the occurrence of pacemaker syndrome. Where patients with optimized AV synchrony have shown great results of implantation and very low incidence of pacemaker syndrome than those with suboptimal AV synchronization.

Individuals with LGL syndrome do not carry an increased risk of sudden death. The only morbidity associated with the syndrome is the occurrence of paroxysmal episodes of tachycardia which may be of several types, including sinus tachycardia, supraventricular tachycardia, atrial fibrillation, atrial flutter, or even ventricular tachycardia.

HFpEF is typically diagnosed with echocardiography. Techniques such as catheterization are invasive procedures and thus reserved for patients with co-morbid conditions or those who are suspected to have HFpEF but lack clear non-invasive findings. Catheterization does represent are more definitive diagnostic assessment as pressure and volume measurements are taken simultaneously and directly. In either technique the heart is evaluated for left ventricular diastolic function. Important parameters include, rate of isovolumic relaxation, rate of ventricular filling, and stiffness.

Frequently patients are subjected to stress echocardiography, which involves the above assessment of diastolic function during exercise. This is undertaken because perturbations in diastole are exaggerated during the increased demands of exercise. Exercise requires increased left ventricular filling and subsequent output. Typically the heart responds by increasing heart rate and relaxation time. However, in patients with HFpEF both responses are diminished due to increased ventricular stiffness. Testing during this demanding state may reveal abnormalities that are not as discernible at rest.

Ambulatory monitoring of the electrocardiogram (ECG) may be necessary because arrhythmias are transient. The ECG may show any of the following:

- Inappropriate sinus bradycardia

- Sinus arrest

- Sinoatrial block

- Tachy-Brady Syndrome

- Atrial fibrillation with slow ventricular response

- A prolonged asystolic period after a period of tachycardias

- Atrial flutter

- Ectopic atrial tachycardia

- Sinus node reentrant tachycardia

- Wolff-Parkinson-White syndrome

Electrophysiologic tests are no longer used for diagnostic purposes because of their low specificity and sensitivity. Cardioinhibitory and vasodepressor forms of sick sinus syndrome may be revealed by tilt table testing.

A doctor will listen to the heart with stethoscope. A "tumor plop" (a sound related to movement of the tumor), abnormal heart sounds, or a murmur similar to the mid-diastolic rumble of mitral stenosis may be heard. These sounds may change when the patient changes position.

Right atrial myxomas rarely produce symptoms until they have grown to be at least 13 cm (about 5 inches) wide.

Tests may include:

- Echocardiogram and Doppler study

- Chest x-ray

- CT scan of chest

- Heart MRI

- Left heart angiography

- Right heart angiography

- ECG—may show atrial fibrillation

Blood tests:

A FBC may show anemia and increased WBCs (white blood cells). The erythrocyte sedimentation rate (ESR) is usually increased.

Diagnosis is typically made via echocardiography. Patients will demonstrate normal systolic function, diastolic dysfunction, and a restrictive filling pattern. 2-dimensional and Doppler studies are necessary to distinguish RCM from constrictive pericarditis. Cardiac MRI and transvenous endomyocardial biopsy may also be necessary in some cases. Reduced QRS voltage on EKG may be an indicator of amyloidosis-induced restrictive cardiomyopathy.

LAE is suggested by an electrocardiogram (ECG) that has a pronounced notch in the P wave. However, if atrial fibrillation is present, a P wave would not be present. In any case, LAE can be diagnosed and measured using an echocardiogram (ECHO).

Characterizing the size of the left atrium according to its volume is preferred over a single linear dimension since enlargement can be different for different directions. For example, because of the smaller distance in the thoracic cavity between the sternum and spine, compared to the other directions, less room exists for enlargement of the left atrium along the anteroposterior axis. By approximating the shape of the left atrium as an ellipsoid, its volume can be calculated from measurements of its dimensions along three perpendicular directions.

Indexing the left atrial volume to body surface area (volume/BSA) is recommended by the American Society of Echocardiography and the European Association of Echocardiography. The values for volume/BSA in the following table are the best validated, and are the same for both men and women.

There are no specific diagnostic criteria for TIC, and it can be difficult to diagnose for a number of reasons. First, in patients presenting with both tachycardia and cardiomyopathy, it can be difficult to distinguish which is the causative agent. Additionally, it can occur in patients with or without underlying structural heart disease. Previously normal left ventricular ejection fraction or left ventricular systolic dysfunction out of proportion to a patient’s underlying cardiac disease can be important clues to possible TIC. The diagnosis of TIC is made after excluding other causes of cardiomyopathy and observing resolution of the left ventricular systolic dysfunction with treatment of the tachycardia.

Specific tests that can be used in the diagnosis and monitoring of TIC include:

- electrocardiography (EKG)

- Continuous cardiac rhythm monitoring (e.g. Holter monitor)

- echocardiography

- Radionuclide imaging

- Endomyocardial biopsy

- Cardiac magnetic resonance imaging (CMR)

- N-terminal pro-B-type natriuretic peptide (NT-pro BNP)

Cardiac rhythm monitors can be used to diagnose tachyarrhythmias. The most common modality used is an EKG. A continuous rhythm monitor such as a Holter monitor can be used to characterize the frequency of a tachyarrhythmia over a longer period of time. Additionally, some patients may not present to the clinical setting in an abnormal rhythm, and continuous rhythm monitor can be useful to determine if an arrhythmia is present over a longer duration of time.

To assess cardiac structure and function, echocardiography is the most commonly available and utilized modality. In addition to decreased left ventricular ejection fraction, studies indicate that patients with TIC may have a smaller left ventricular end-diastolic dimension compared to patients with idiopathic dilated cardiomyopathy. Radionuclide imaging can be used as a non-invasive test to detect myocardial ischemia. Cardiac MRI has also been used to evaluate patients with possible TIC. Late-gadolinium enhancement on cardiac MRI indicates the presence of fibrosis and scarring, and may be evidence of cardiomyopathy not due to tachycardia. A decline in serial NT-pro BNP with control of tachyarrhythmia indicates reversibility of the cardiomyopathy, which would also suggest TIC.

People with TIC display distinct changes in endomyocardial biopsies. TIC is associated with the infiltration of CD68 macrophages into the myocardium while CD3 T-cells are very rare. Furthermore, patients with TIC display significant fibrosis due to collagen deposition. The distribution of mitochondria has found to be altered as well, with an enrichment at the intercalated discs (EMID-sign).

TIC is likely underdiagnosed due to attribution of the tachyarrhythmia to the cardiomyopathy. Poor control of the tachyarrhythmia can result in worsening of heart failure symptoms and cardiomyopathy. Therefore, it is important to aggressively treat the tachyarrhythmia and monitor patients for resolution of left ventricular systolic dysfunction in cases of suspected TIC.

It is named for Mary Holt and Samuel Oram, who published a paper on it in 1960.

For proper diagnosis of situs ambiguous, cardiac and non-cardiac features must be evaluated. Diagnostic criteria for atrial isomerism includes observation of symmetry of thoracic visceral organs upon echocardiogram, arrhythmia upon electrocardiogram, and chest x-ray for confirmation of the heart's location across the left-right axis. In addition, a series of gastrointestinal tests can be conducted for observation of intestinal malrotation, as well as a scan of the liver and spleen for biliary function.

LGL syndrome is diagnosed on the basis of the surface EKG in a symptomatic individual with a PR interval less than or equal to 0.12 second (120 ms) with normal QRS complex configuration and duration. It can be distinguished from WPW syndrome because the delta waves seen in WPW syndrome are not seen in LGL syndrome. It is a clinical diagnosis that came about before the advent of electrophysiology studies. Be aware, however, that not all WPW EKG's have a delta wave; the absence of a delta wave does not conclusively rule out WPW.

Although its cause is poorly understood, situs ambiguous has been linked to family history of malformations and maternal cocaine use, suggesting both genetic and environmental factors play a role. Several genes in the TGF-beta pathway, which controls left-right patterning of viseral organs across the body axis, have been indicated in sporadic and familial cases of atrial isomerism.

There does not appear to be a screening method for prevention of heterotaxy syndrome. However, genetic testing in family members that display atrial isomerism or other cardiac malformations may help to discern risk for additional family members, especially in X-linked causes of heterotaxy syndrome.

A chest radiogram can be given to a patient to determine:

- Pulmonary plethora: the test will help to determine if there is a left-to-right shunt meaning the blood is flowing from the left atrium to the right through a hole between the two atria.

- Mild left atrial enlargement: the test will help to determine if the left atrium is enlarged due to alternate blood flows

- Right ventricular enlargement: the test will help to determine if the ventricle is enlarged due to a surge of blood above normal or if the ventricle is having to work harder than normal to pump blood out of the ventricle.

- Pulmonary artery enlargement: the test will help to determine if there is a large volume of blood in the pulmonary veins and arteries than normal

- Mitral Valve calcification late in life: the test will help to determine if the mitral valve or flaps are becoming hardened and losing their floppiness.

- pulmonary vascular congestion, marked left atrial enlargement: the test will help to determine if there is a sign of MS and small ASD and how severe both are.

A physical examination will be done to check for abnormal heart sounds, condition of heart, blood pressure, lungs, palpitations, edema, weight gain, ascites, or any other abnormal symptoms. Blood may also be drawn to help determine the cause of fatigue, determination of ascites, other health problems that maybe closely related to cause the symptoms such as kidney, liver, immune (signs of rheumatic fever), abnormal glucose levels.

In otherwise healthy patients, occasional premature atrial contractions are a common and normal finding and do not indicate any particular health risk. Rarely, in patients with other underlying structural heart problems, PACs can trigger a more serious arrhythmia such as atrial flutter or atrial fibrillation. In otherwise healthy people, PACs usually disappear with adolescence.

In general, the minimal evaluation of atrial fibrillation should be performed in all individuals with AF. The goal of this evaluation is to determine the general treatment regimen for the individual. If results of the general evaluation warrant it, further studies may then be performed.

Limited studies have suggested that screening for atrial fibrillation in those 65 years and older increases the number of cases of atrial fibrillation detected.

If undiagnosed (or untreated), Stokes–Adams attacks have a 50% mortality within a year of the first episode. The prognosis following treatment is very good.