Two patients, 14 and 18 yr old, with congenital left ventricular right atrial communication through a defect in the tricuspid valve were studied by echocardiography. Proof was obtained by angiocardiography and surgery in one and ultrasonic contrast injection and angiocardiography in the other. Both presented clinically as uncomplicated ventricular septal defects. Echocardiography consistently demonstrated a high frequency, low amplitude flutter of the tricuspid valve in systole and none in diastole. Following surgical correction of the defect in one patient, there was complete disappearance of the systolic flutter. Systolic flutter has not been observed with tricuspid incompetence nor with other forms of ventricular septal defects. Fistulous communication from the aorta to the right atrium just above the tricuspid valve did not demonstrate systolic flutter in one patient studied. Tricuspid valve systolic flutter appears to be caused by the passage of the left ventricular jet of blood into the right atrium through a defect in the tricuspid valve. Echocardiographic study of the tricuspid valve is of value in the recognition of the congenital left ventricular right atrial communication.