The findings in four patients with marked paradoxical septal motion and an unusual early diastolic sound are presented. Each patient had markedly abnormal right ventricular function. Phonocardiograms, apexcardiograms, and echocardiograms showed the sound to precede the expected timing of a third heart sound and to coincide with the peak leftward displacement of the paradoxically moving septum in early diastole. In two patients the sound was also accompanied by third and fourth heart sounds, revealing a total of five heart sounds on phonocardiographic studies. The sound appeared to originate from the sudden deceleration of the septal mass as it moved leftward during ventricular relaxation.