Rheumatic fever is a delayed consequence of an untreated upper respiratory infection with group A streptococci . The disease can cause serious, debilitating damage to the heart and involve other tissues. Only a small percentage of all people who have streptococcal pharyngitis will actually develop acute rheumatic fever. In Western countries, it became somewhat rare since the 1960s, likely due to the widespread use of antibiotics to treat streptococcus infections. There have been a few outbreaks since the 1980s. Although the disease seldom occurs in the US, it is serious and has a mortality of 2–5%.

Initially, rheumatic fever is acute. The major symptoms of rheumatic fever are: carditis, polyarthritis, chorea, subcutaneous nodules, and a rash called erythema marginatum.

Carditis is the most significant manifestation of rheumatic fever because it may cause permanent organ damage or death. Carditis is frequently mild or asymptomatic and therefore difficult to detect. Although not fully understood, a person's immune system response to a streptococcal infection appears to cause tissue degeneration, most frequently heart valve tissue, and subsequently, cardiac disability or death.

Polyarthritis is arthritis in a number of joints at a time. Subcutaneous nodules are firm, painless lesions that occur over bony surfaces just under the skin. Erythema marginatum is a rash that appears mostly on the trunk and extremities.

The peak age of incidence for rheumatic fever is 5 to 15 years, but cases do occur in adults. Acute rheumatic fever is rare in children less than 4 years of age.

There is a latent period of 1 to 5 weeks (average 19 days) between streptococcal pharyngitis and the initial episode of acute rheumatic fever. The average duration of an attack of acute rheumatic fever is 3 months or longer.

There are no specific laboratory tests to diagnose acute rheumatic fever. In general, rheumatic fever can be diagnosed with documentation of a recent infection with group A streptococcal infection and observation of one or more of the major symptoms.

Prevention of rheumatic fever involves prompt, accurate diagnosis and effective treatment of streptococcal pharyngitis especially in school-aged children and others who live in crowded conditions such as the military and large households.