Children may experience abnormal heart murmurs resulting from congenital heart disease, but adults typically have them when dealing with a heart valve problem, according to Mayo Clinic. Congenital heart diseases typically occur from a hole in the heart or a heart valve abnormality.
Adults may experience abnormal heart murmurs based on certain health conditions, such as rheumatic fever, valve calcification, mitral valve prolapse and endocarditis. Other types of heart murmurs, called innocent murmurs, occur when blood moves more quickly through the heart. Drivers of innocent murmurs include fever, pregnancy, heavy physical activity, heart surgery, limited healthy red blood cells and excessive thyroid hormone, reports Mayo Clinic.