Types of heart murmurs include innocent murmurs and abnormal murmurs, according to Mayo Clinic. While innocent murmurs result from excessively rapid flow of blood through the heart, abnormal murmurs commonly occur as a result of congenital heart defects in children. Abnormal heart murmurs in adults and older children may also result from conditions such as valve calcification, rheumatic fever and endocarditis, which cause damage to the heart's structure.
Rapid blood flow through the heart may result from conditions such as fever, pregnancy, rapid growth due to adolescence, overactive thyroid gland and anemia, which is a condition in which the body tissues fail to receive sufficient oxygen supply due to inadequate red blood cells, notes Mayo Clinic.
Cardiac shunts and heart valve abnormalities are congenital effects that commonly cause abnormal heart murmurs, states Mayo Clinic. Cardiac shunts are holes in the heart, which occur in various parts of the heart, in various sizes as a result of an abnormality in the flow of blood between the blood vessels or heart chambers. The seriousness of cardiac shunts depends on the part of the heart they attack and size of the holes. Heart valve abnormalities that may result in abnormal heart murmurs include stenosis, which is failure of the heart valves to pass enough blood, and mitral valve prolapse, a condition in which the cardiac valves regurgitate blood.