Two heart sounds resulting from cardiac contraction are normally heard through a stethoscope placed on the chest wall. The first sound, a soft low-pitched lub, is associated with closure of the atrioventricular (AV) valves; the second sound, a louder dup, is associated with closure of the pulmonary and aortic valves. The lub marks the onset of systole while the dup occurs at the onset of diastole. These sounds, which result from vibrations caused by the closing valves, are perfectly normal, but other sounds, known as heart murmurs, can be a sign of heart disease.
Murmurs can be produced by blood flowing rapidly in the usual direction through an abnormally narrowed valve (stenosis), by blood flowing backward through a damaged, leaky valve (insufficiency), or by blood flowing between the two atria or two ventricles through a small hole in the wall separating them (called a septal defect). The exact timing and location of the murmur provide the physician with a powerful diagnostic clue. For example, a murmur heard throughout systole suggests a stenotic pulmonary or aortic valve, an insufficient AV valve, or a hole in the interventricular septum. In contrast, a murmur heard during diastole suggests a stenotic AV valve or an insufficient pulmonary or aortic valve.