Ten patients with valvular pulmonic stenosis were studied by simultaneous external phonocardiograms and intracardiac pressure recordings during successive respiratory cycles to examine the mechanism of the respiratory variation in the ejection click. Selective cineangiograms were perforned in four. During inspiration right ventricular end-diastolic pressure (RVEDP) exceeded the pressure in the pulmonary artery (+ 2.7 mm) and no ejection click was recorded. During expiration RVEDP was lower than

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... the pressure in the pulmonary artery (-3.6 mm) and a click was recorded. The click was present throughout the respiratory cycle when pulmonary artery diastolic pressure consistently exceeded RVEDP. Clicks were associated with sudden "doming" of the valve demonstated by cineangiography. These data support the valvular origin of the ejection click in pulmonic stenosis and provide the following explanation for the respiratory variation: Inspiratory increase in venous return causes the valve leaflets to move to an open or "domed" position. Ventricular systole at this time produces no sound since there is no slack. With expiration pulmonary artery pressure exceeds RVEDP. Ventricular systole at this time produces an opening motion of the closed, slack leaflets. The click occurs when the opening motion is suddenly checked.