By monitoring arterial blood flow signals across the chest wall in the area of the heart and timing them to the electrocardiogram or the heart sounds, it is often possible to differentiate between coronary artery flow and systemic artery flow. A Doppler ultrasound technique was used for the postoperative follow-up coronary artery reconstruction in ten patients suffering from intractable angina pectoris. Pre-operative coronary angiography showed stenosis or occlusion of the coronary arteries in all the patients. The ultrasound measurements were made pre-, per- and postoperatively with the Doppler flowmeter. Flow signals in all patients could be visualized on sonagrams. There was no postoperative occlusion as proved by postoperative angiography. The signals recorded outside the chest were smaller than those recorded directly from the arteries inside the chest, due to attenuation of the audio signal passing through the tissues of the chest wall. The characteristic pattern of postoperative bypass blood flow was a broad continuous flow over the diastole. The noninvasive character of ultrasound techniques and the safety of the method make Doppler ultrasound scanning an important adjunct to patient monitoring and renders it valuable for post-operative follow-up of arterial graft patency.