To provide additional information on the relation of valvular events to the principal components of the first heart sound (s1), combined echocardiograms and phonocardiograms were recorded in 49 subjects, chosen because of audible splitting of S1 or a combination of S1 and an ejection sound. The subjects included 14 normal persons, 16 patients with a variety of predominantly right-sided heart conditions, 7 with mitral stenosis, 3 with pulmonary stenosis and 9 with aortic valve disease or systemic hypertension. A precise relation was found between completion of closure of the atrioventricular (A-V) valves manifested in the echocardiogram and the high-frequency components of S1 (M1 and T1). The average time from the Q wave of the electrocardiogram to M1 was 0.06 plus or minus 0.003 second and the Q-T1 interval was 0.09 plus or minus 0.002 second. In mitral stenosis the Q-M1 interval was delayed to 0.10 plus or minus 0.005 second, resulting in some instances in reversed splitting of S1. In pulmonary stenosis, the ejection sound occurred 0.10 plus or minus 0.003 second from the Q wave. In 7 of the 16 patients with various right-sided abnormalities, but without valvular stenosis, an ejection sound of pulmonary origin occurred 0.18 plus or minus 0.012 second from the Q wave. In the nine patients with aortic valve disease or systemic hypertension, the time from the Q wave to the aortic ejection sound was 0.13 plus or minus 0.004 second. With only two exceptions the ejection sounds of aortic and plumonary origin coincided exactly with achievement of a fully opened position of the respective semilunar valve. Our findings support the postulate that M1, T1 and the ejection sounds occur in association with closing or opening of valves with consequent sudden deceleration or acceleration of a column of blood that, in turn, results in vibrations of the cardiohemic system and audible sounds.