Murmurs and Abnormal Heart Sounds

Abstract

Heart sounds are caused by audible vibrations of cardiohemic tissues. Normal heart sounds are the first sound (S1), timed with closure and tensing of the atrioventricular (AV) valves and associated structures at the onset of systole, and the second sound (S2), associated with closure of the aortic and pulmonic valves following ejection. Many sounds generated by the heart are too low in frequency and intensity to be audible, even with the stethoscope. Murmurs are defined as audible vibrations of prolonged duration occurring during a normally silent period of the cardiac cycle. Pathologic causes of murmurs usually relate to valvular insufficiency, narrowing of valves or surrounding regions, or shunts. The Point of Maximal Intensity (PMI) of a murmur usually is indicated by the hemithorax and intercostal space or valve area where it is located, or by the terms apex or base. A murmur can be described by its phonocardiographic shape, which arises from the hemodynamic forces that generate it.