Four patients who had had a Fontan type of procedure for tricuspid atresia 23, 6, 6, and 11 months previously were investigated by ambulatory electrocardiographic recording and simultaneous recording of the jugular venous pressure and echocardiogram of the conduit or pulmonary valve. All had been considerably improved by the operation. In 1 patient episodes of supraventricular tachycardia were recorded but no rhythm disturbance was detected in the other 3. Pulmonary blood flow was shown to be pulsatile and atrial systole is an important factor in this. The conduit valve showed delayed opening and slow closure suggesting that its presence in the pulmonary circuit may be unnecessary.