Murmurs are abnormal heart sounds that are heard using a stethoscope. The sounds most commonly originate from the abnormal movement of blood across valves and between cardiac chambers. When this occurs, turbulence results, which produces vibrations in the chambers of the heart or outflow vessels (aorta or pulmonary artery) that are detected as audible, low frequency sounds. Murmurs are distinct from the normal heart sounds that represent the closure of semilunar and atrioventricular valves during the cardiac cycle.
Murmurs can be divided into two general classifications related to origin: those caused by valve defects and those caused by interchamber defects that permit an abnormal flow of blood between cardiac chambers. In order to understand the pathophysiology of murmurs, it is first necessary to understand the physical factors governing the flow of blood (i.e., hemodynamics), the basic anatomy of the heart, and the sequence of events that occurs as the heart contracts and relaxes (i.e., cardiac cycle).