About 33 million people are affected by rheumatic heart disease with an additional 47 million having asymptomatic damage to their heart valves. As of 2010 globally it resulted in 345,000 deaths, down from 463,000 in 1990.

In Western countries, rheumatic fever has become fairly rare since the 1960s, probably due to the widespread use of antibiotics to treat streptococcus infections. While it has been far less common in the United States since the beginning of the 20th century, there have been a few outbreaks since the 1980s. Although the disease seldom occurs, it is serious and has a case-fatality rate of 2–5%.

Rheumatic fever primarily affects children between ages 5 and 17 years and occurs approximately 20 days after strep throat. In up to a third of cases, the underlying strep infection may not have caused any symptoms.

The rate of development of rheumatic fever in individuals with untreated strep infection is estimated to be 3%. The incidence of recurrence with a subsequent untreated infection is substantially greater (about 50%). The rate of development is far lower in individuals who have received antibiotic treatment. Persons who have suffered a case of rheumatic fever have a tendency to develop flare-ups with repeated strep infections.

The recurrence of rheumatic fever is relatively common in the absence of maintenance of low dose antibiotics, especially during the first three to five years after the first episode. Recurrent bouts of rheumatic fever can lead to valvular heart disease. Heart complications may be long-term and severe, particularly if valves are involved. In countries in Southeast-Asia, sub-saharan Africa, and Oceania, the percentage of people with rheumatic heart disease detected by listening to the heart was 2.9 per 1000 children and by echocardiography it was 12.9 per 1000 children.

Particulate matter has been studied for its short- and long-term exposure effects on cardiovascular disease. Currently, PM is the major focus, in which gradients are used to determine CVD risk. For every 10 μg/m of PM long-term exposure, there was an estimated 8–18% CVD mortality risk. Women had a higher relative risk (RR) (1.42) for PM induced coronary artery disease than men (0.90) did. Overall, long-term PM exposure increased rate of atherosclerosis and inflammation. In regards to short-term exposure (2 hours), every 25 μg/m of PM resulted in a 48% increase of CVD mortality risk. In addition, after only 5 days of exposure, a rise in systolic (2.8 mmHg) and diastolic (2.7 mmHg) blood pressure occurred for every 10.5 μg/m of PM. Other research has implicated PM in irregular heart rhythm, reduced heart rate variability (decreased vagal tone), and most notably heart failure. PM is also linked to carotid artery thickening and increased risk of acute myocardial infarction.

Cardiovascular disease affects low- and middle-income countries even more than high-income countries. There is relatively little information regarding social patterns of cardiovascular disease within low- and middle-income countries, but within high-income countries low income and low educational status are consistently associated with greater risk of cardiovascular disease. Policies that have resulted in increased socio-economic inequalities have been associated with greater subsequent socio-economic differences in cardiovascular disease implying a cause and effect relationship. Psychosocial factors, environmental exposures, health behaviours, and health-care access and quality contribute to socio-economic differentials in cardiovascular disease.

Carditis is the inflammation of the heart or its surroundings. The plural of carditis is carditides.

It is usually studied and treated by specifying it as:

- Pericarditis is the inflammation of the pericardium

- Myocarditis is the inflammation of the heart muscle

- Endocarditis is the inflammation of the endocardium

- Pancarditis is the inflammation of the entire heart: the epicardium, the myocardium and the endocardium

- Reflux carditis refers to a possible outcome of esophageal reflux (also known as GERD), and involves inflammation of the esophagus/stomach mucosa

Some patients develop significant carditis which manifests as congestive heart failure. This requires the usual treatment for heart failure: ACE inhibitors, diuretics, beta blockers, and digoxin. Unlike normal heart failure, rheumatic heart failure responds well to corticosteroids.

The frequency of tamponade is unclear. One estimate from the United States places it at 2 per 10,000 per year. It is estimated to occur in 2% of those with stab or gunshot wounds to the chest.

Cardiac tamponade is caused by a large or uncontrolled pericardial effusion, i.e. the buildup of fluid inside the pericardium. This commonly occurs as a result of chest trauma (both blunt and penetrating), but can also be caused by myocardial rupture, cancer, uremia, pericarditis, or cardiac surgery, and rarely occurs during retrograde aortic dissection, or while the person is taking anticoagulant therapy. The effusion can occur rapidly (as in the case of trauma or myocardial rupture), or over a more gradual period of time (as in cancer). The fluid involved is often blood, but pus is also found in some circumstances.

Causes of increased pericardial effusion include hypothyroidism, physical trauma (either penetrating trauma involving the pericardium or blunt chest trauma), pericarditis (inflammation of the pericardium), iatrogenic trauma (during an invasive procedure), and myocardial rupture.

Athlete's heart is not dangerous for athletes (though if a nonathlete has symptoms of bradycardia, cardiomegaly, and cardiac hypertrophy, another illness may be present). Athlete's heart is not the cause of sudden cardiac death during or shortly after a workout, which mainly occurs due to hypertrophic cardiomyopathy, a genetic disorder.

No treatment is required for people with athletic heart syndrome; it does not pose any physical threats to the athlete, and despite some theoretical concerns that the ventricular remodeling might conceivably predispose for serious arrhythmias, no evidence has been found of any increased risk of long-term events. Athletes should see a physician and receive a clearance to be sure their symptoms are due to athlete’s heart and not another heart disease, such as cardiomyopathy. If the athlete is uncomfortable with having athlete's heart or if a differential diagnosis is difficult, deconditioning from exercise for a period of three months allows the heart to return to its regular size. However, one long-term study of elite-trained athletes found that dilation of the left ventricle was only partially reversible after a long period of deconditioning. This deconditioning is often met with resistance to the accompanying lifestyle changes. The real risk attached to athlete's heart is if athletes or nonathletes simply assume they have the condition, instead of making sure they do not have a life-threatening heart illness.

Because several well-known and high-profile cases of athletes experiencing sudden unexpected death due to cardiac arrest, such as Reggie White and Marc-Vivien Foé, a growing movement is making an effort to have both professional and school-based athletes screened for cardiac and other related conditions, usually through a careful medical and health history, a good family history, a comprehensive physical examination including auscultation of heart and lung sounds and recording of vital signs such as heart rate and blood pressure, and increasingly, for better efforts at detection, such as an electrocardiogram.

An electrocardiogram (ECG) is a relatively straightforward procedure to administer and interpret, compared to more invasive or sophisticated tests; it can reveal or hint at many circulatory disorders and arrhythmias. Part of the cost of an ECG may be covered by some insurance companies, though routine use of ECGs or other similar procedures such as echocardiography (ECHO) are still not considered routine in these contexts. Widespread routine ECGs for all potential athletes during initial screening and then during the yearly physical assessment could well be too expensive to implement on a wide scale, especially in the face of the potentially very large demand. In some places, a shortage of funds, portable ECG machines, or qualified personnel to administer and interpret them (medical technicians, paramedics, nurses trained in cardiac monitoring, advanced practice nurses or nurse practitioners, physician assistants, and physicians in internal or family medicine or in some area of cardiopulmonary medicine) exist.

If sudden cardiac death occurs, it is usually because of pathological hypertrophic enlargement of the heart that went undetected or was incorrectly attributed to the benign "athletic" cases. Among the many alternative causes are episodes of isolated arrhythmias which degenerated into lethal VF and asystole, and various unnoticed, possibly asymptomatic cardiac congenital defects of the vessels, chambers, or valves of the heart. Other causes include carditis, endocarditis, myocarditis, and pericarditis whose symptoms were slight or ignored, or were asymptomatic.

The normal treatments for episodes due to the pathological look-alikes are the same mainstays for any other episode of cardiac arrest: Cardiopulmonary resuscitation, defibrillation to restore normal sinus rhythm, and if initial defibrillation fails, administration of intravenous epinephrine or amiodarone. The goal is avoidance of infarction, heart failure, and/or lethal arrhythmias (ventricular tachycardia, ventricular fibrillation, asystole, or pulseless electrical activity), so ultimately to restore normal sinus rhythm.

A drug-resistant strain of scarlet fever, resistant to macrolide antibiotics such as erythromycin, but retaining drug-sensitivity to beta-lactam antibiotics such as penicillin, emerged in Hong Kong in 2011, accounting for at least two deaths in that city—the first such in over a decade. About 60% of circulating strains of the group A "Streptococcus" which cause scarlet fever in Hong Kong are resistant to macrolide antibiotics, says Professor Kwok-yung Yuen, head of Hong Kong University's microbiology department. Previously, observed resistance rates had been 10–30%; the increase is likely the result of overuse of macrolide antibiotics in recent years.

Scarlet fever occurs equally in both males and females. Children are most commonly infected, typically between 5–15 years old. Although streptococcal infections can happen at any time of year, infection rates peak in the winter and spring months, typically in colder climates.

The morbidity and mortality of scarlet fever has declined since the 18th and 19th century when there were epidemics caused by this disease. Around 1900 the mortality rate in multiple places reached 25%. In The improvement in prognosis can be attributed to the use of penicillin in the treatment of this disease. The frequency of scarlet fever cases has also been declining over the past century however, there have been several reported outbreaks of the disease in various countries in the past decade. The reason for these recent increases remains unclear in the medical community.

Wissler's syndrome (or Wissler's disease or Wissler-Fanconi syndrome) is a rheumatic disease that has a similar presentation to sepsis. It is sometimes considered closely related to Still's disease. It is named for Guido Fanconi and Hans Wissler It was first described by Wissler in 1944 and Fanconi in 1946. Single observations by E. Uhse in 1943 («Febris maculosa intermittens»), Fykow in 1929 and Nowak in 1942.

Children and adolescents are most frequently affected; age in the reported cases varied from 5 to 17 years.

Fifty percent of patients with acute Sydenham's chorea spontaneously recover after two to six months whilst mild or moderate chorea or other motor symptoms can persist for up to and over two years in some cases. Sydenham's is also associated with psychiatric symptoms with obsessive compulsive disorder being the most frequent manifestation.

In addition to an OCD or tic disorder diagnosis, children may have other symptoms associated with exacerbations such as emotional lability, enuresis, anxiety, and deterioration in handwriting. In the PANDAS model, this abrupt onset is thought to be preceded by a strep throat infection. As the clinical spectrum of PANDAS appears to resemble that of Tourette's syndrome, some researchers hypothesized that PANDAS and Tourette's may be associated; this idea is controversial and a focus for current research.

Sydenham's chorea (SC) or chorea minor (historically referred to as St Vitus's dance) is a disorder characterized by rapid, uncoordinated jerking movements primarily affecting the face, hands and feet. Sydenham's chorea results from childhood infection with Group A beta-haemolytic "Streptococcus" and is reported to occur in 20–30% of patients with acute rheumatic fever (ARF). The disease is usually latent, occurring up to 6 months after the acute infection, but may occasionally be the presenting symptom of rheumatic fever. Sydenham's chorea is more common in females than males and most patients are children, below 18 years of age. Adult onset of Sydenham's chorea is comparatively rare and the majority of the adult cases are associated with exacerbation of chorea following childhood Sydenham's chorea.

Erythema marginatum is a type of erythema (redness of the skin or mucous membranes) involving pink rings on the torso and inner surfaces of the limbs which come and go for as long as several months. It is found primarily on extensor surfaces.

An association with bradykinin has been proposed in the case of hereditary angioedema.

Pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS) is a hypothesis that there exists a subset of children with rapid onset of obsessive-compulsive disorder (OCD) or tic disorders and these symptoms are caused by group A beta-hemolytic streptococcal (GABHS) infections. The proposed link between infection and these disorders is that an initial autoimmune reaction to a GABHS infection produces antibodies that interfere with basal ganglia function, causing symptom exacerbations. It has been proposed that this autoimmune response can result in a broad range of neuropsychiatric symptoms.

The PANDAS hypothesis was based on observations in clinical case studies at the US National Institutes of Health and in subsequent clinical trials where children appeared to have dramatic and sudden OCD exacerbations and tic disorders following infections. There is supportive evidence for the link between "streptococcus" infection and onset in some cases of OCD and tics, but proof of causality has remained elusive. The PANDAS hypothesis is controversial; whether it is a distinct entity differing from other cases of Tourette syndrome (TS)/OCD is debated.

PANDAS has not been validated as a disease entity; it is not listed as a diagnosis by the International Statistical Classification of Diseases and Related Health Problems (ICD) or the "Diagnostic and Statistical Manual of Mental Disorders" (DSM).

It occurs in less than 5% of patients with rheumatic fever, but is considered a major Jones criterion when it does occur. The four other major criteria include carditis, polyarthritis, Sydenham's Chorea, and subcutaneous nodules. In this case, it is often associated with Group A streptococcal infection, otherwise known as "Streptococcus pyogenes" infection, which can be detected with an ASO titer.

It is an early feature of rheumatic fever and not pathognomonic of it. It may be associated with mild myocarditis (inflammation of heart muscle). It is also seen in conditions like allergic drug reactions, sepsis and glomerulonephritis.

It often occurs as a harbinger of attacks in hereditary angioedema. In this case it may occur several hours or up to a day before an attack.