Rheumatic fever is a disease characterized by the inflammation of many connective tissues throughout the body, particularly in the heart, joints and central nervous system (the brain and spinal cord). Rheumatic fever is usually caused by an untreated infection with streptococcus bacteria, such as in  strep throat or scarlet fever.  

Rheumatic fever usually develops roughly 20 days after the streptococcus infection and can damage a wide variety of tissues in the body, especially the heart valves. It is one of the major causes of heart valve disease in the world. It can also damage the chambers and other vessels of the heart. Untreated, the damage to the heart will become permanent, at which point rheumatic fever is called rheumatic heart disease. Rheumatic heart disease may involve one or more of the following:

Rheumatic fever is more common in children aged from 6 to 15. Before the widespread availability of antibiotics in the United States, rheumatic fever was the most common cause of valve damage. However, cases of rheumatic fever are now relatively rare. According to the National Institutes of Health (NIH) roughly three percent of untreated streptococcus infections develop into rheumatic fever. 

The mortality rate for rheumatic heart disease varies greatly from country to country. In more developed countries, mortality is 0.5 per 100,000. In less developed countries, mortality reaches 8.2 per 100,000, accounting for millions of deaths globally every year. Much of these are due to the lack of antibiotics in developing countries and difficulties in diagnosing the disease.