DURING the past 18 years a search has been made for improved methods of relieving myocardial ischemia. A review of pathological knowledge of coronary artery disease showed that the disease is diffusely distributed through out the coronary arteries in their epicardial courses involving particularly the main stems of the major coronary arteries. In 1941, Schlesinger1 demonstrated as many as 2.5 lesions per diseased heart (Fig. 1). and that 70 per cent of the lesions were within the area of the coronary ossa. In short, the disease effects a stranglehold upon the coronary artery inflow tract (Fig. 2) which is so diffuse that direct surgical relief of coronary artery obstruction is im practicable.

Because of these facts our efforts have been mainly directed toward the development of bypass operations through which coronary oxygenated blood is carried past points of coronary artery obstruction to be introduced into the comparatively intact arteriolar system. In the bypass operation, the patient's original coronary arterial tree is untouched, thus permitting operations to be performed in far-advanced cases of coronary artery obstructive disease with a low operative mortality. The internal mammary artery implant operation was the first bypass op eration developed by us in 1946. 2 Experience has shown that the artery re mains open in approximately 70 per cent of human cases when examined up to 10 years postoperatively. It is capable of supplying oxygenated blood to the left ventricle in sufficient quantities to maintain its health when there is oc clusion of the major left coronary arteries. It is, however, not large enough to supply the entire heart when both right and left coronary arteries become diseased, ie, when triple coronary artery disease is present. 3'16