Final answer:
Rheumatic fever primarily affects the mitral valve and can also involve the aortic, tricuspid, and pulmonary valves, leading to heart murmur due to scarred and stiff valve leaflets.
Step-by-step explanation:
Rheumatic fever is an autoimmune disease that primarily affects heart valves, particularly the mitral valve, but can also involve the aortic valve, tricuspid valve, and to a lesser extent, the pulmonary valve. The disease is caused by an inflammatory response to Streptococcus pyogenes infection, which can result in carditis and chronic damage to the heart valves. This condition is characterized by the development of a heart murmur due to the scarring and stiffness of the valve leaflets. Recurrent attacks of rheumatic fever, especially within the first 3-5 years following an initial attack, can exacerbate the damage to the heart valves, with the mitral valve being most frequently affected.