Since Heberden's classic description of angina pectoris in 1768, a satisfactory treatment has been sought. Nitroglycerin, which is the standard treatment, may have unpleasant side effects due to vasodilatation, and its duration of action is relatively short. From the rapid turnover of a multitude of alleged long-acting coronary vasodilators marketed, it is apparent that an ideal compound which is both effective and devoid of side effects has not been found. Fischer and Roch reported in 1951 the synthesis of a new group of compounds with two pyrimidine rings. One of these compounds, dipyridamole (Persantine), was subsequently shown to produce a significant increase in coronary blood flow1and an increase in intercoronary anastomoses in dogs with surgically induced coronary artery constriction.2 In patients with angina pectoris, several uncontrolled, or only partially double-blind, studies have indicated that dipyridamole produced subjective improvement.3-6In contrast, four double-blind studies7-10have indicated