Factors responsible for normal splitting of first heart sound. High-speed echophonocardiographic study of valve movement.

exact coincidence between the final halt of the closing mitral valve and the onset of the first major component of the first sound, and between tricuspid valve closure and the onset of the second group of high-frequency vibrations (Burggraf and Craige, 1974; Leatham and Leech, 1974; Waider and Craige, 1975). Using echophonocardiography it is possible for the first time to identify the two components with certainty, and it is therefore opportune to re-examine the factors responsible for physiological splitting of the first heart sound.