heart sounds

Heart Sounds

First sound (S1): described as a “low, slightly prolonged ‘lub’” (Ganong 569); vibrations caused by the closure of the mitral and tricuspid valves at the beginning of ventricular systole. It is soft when the heart rate is low. Normally, there is no splitting of this sound.
Normal duration: 0.15 s
Normal frequency: 25-45 Hz

Second sound (S2): a “shorter, high-pitched ‘dup’” (Ganong 569); caused by vibrations from the closure of the aortic and pulmonary valves, also known as the semilunar valves, just after the end of ventricular systole. The interval between the aortic and pulmonary valves shutting may split during inspiration (physiologic splitting) or in various diseases
Normal duration: 0.12 s
Normal frequency: 50 Hz
Clinical correlation—with increased respirations, S2 splits due to changes in intrathoracic pressure. The aortic valve closes before the pulmonary valve. (Michael Silverman, “Prehospital heart sounds”, EMSresponder.com)

Third sound (S3): a “soft, low-pitched sound” (Ganong 569); audible about one third of the way through diastole in many young adults. It is probably caused by an inrush of blood during rapid ventricular filling
Normal duration: 0.1 s

Fourth sound (S4): caused by ventricular filling and is usually association with a pathology. It is rarely heard in adults. It may be heard in cases of ventricular hypertrophy, where the ventricles are stiffer, or when atrial pressure is high.