Balloon dilatation of the atherosclerotic lesion damages the endothelium, intima, and media of the artery. This may lead to restenosis via platelet deposition, mural thrombus formation, and intimal proliferation by mechanisms that appear similar to those causing aortocoronary vein graft (ACVG) occlusions. It had been demonstrated that dipyridamole plus aspirin therapy suppressed these mechanisms of ACVG occlusion in the animal model, prolonged a shortened platelet survival in patients with coronary artery disease, and reduced ACVG occlusions in patients both early and late after the operation. Thus, a trial of these drugs in patients undergoing PTCA was a logical and necessary step to reduce the major shortcoming of the initially successful PTCA therapy, namely the high rate of restenosis.