Rheumatic fever can negatively impact numerous tissues around the body of the connective variation, including those of the heart, skin, joints, and brain. When an individual's heart is affected by rheumatic fever, it is usually associated with damage to the mitral valve or aortic valve. Heart valves are structures in the heart made of connective tissues that contain several leaflets. These valve leaflets open and close to allow blood to flow in and out of the chambers correctly.
When the leaflets that make up the heart valves are infected by the bacteria that cause rheumatic fever, they can become damaged and scarred. The damage and scarring of the heart leaflets can cause them to become abnormally stiff or too loose to close properly. The valve abnormalities can cause blood to flow backward or forwards in an irregular and turbulent manner. These irregular movements of the blood in an affected individual's heart can produce a heart murmur.