The first heart sound in normal and ectopic ventricular contractions; mechanism of closure of the A-V valves.

Phasic right atrial and ventricular pressures and heart sounds were simultaneously recorded from dogs with normal and ectopic ventricular contractions. Heart sounds and electrocardiograms were recorded from humans. The first heart sound is significantly delayed in the absence of atrial systole. The time between onset of the ventricular pressure rise due to ventricular contraction and the beginning of the first heart sound is minimal at normal As-Vs intervals. These findings support the view that normally the A-V valves are closed or nearly closed before ventricular systole. In ectopic ventricular beats the A-V valves are closed from an open position by ventricular contraction.