Percutaneous transluminal angioplasty, a balloon catheter technique to recanalize stenotic or occluded arteries, has gained popularity due to its success rate, safety, and relatively low cost as compared with surgical alternatives. Many users of this technique have attempted to optimize the results by the empirical use of various anticoagulants, antiplatelet agents, and vasodilators, but the utility of these agents has not been established and has even been questioned by some. In order to further improve the effectiveness and safety of this procedure, we need to know how to use pharmacological adjuncts to preserve the patency of the recanalized vessel. This objective can best be answered using an appropriate animal model of atherosclerosis, in which the response of the atherosclerotic lesion to controlled drug interventions can be studied. Using a rabbit atherosclerosis model we designed specifically for the investigation of angioplasty, we propose to study the effect of aspirin, heparin, warfarin, verapamil, prostacyclin, ticlopidine, dipyridamole, and dipyridamole plus aspirin on the evolution of focal atherosclerotic lesions undergoing angioplasty and their controls. We will achieve this by measuring patency rate, degree of stenosis, Doppler pressure ratios, and platelet products Thromboxane B2 and low affinity platelet factor 4. In addition, the effect of these drugs on the endothelium will be monitored with 6-Keto PGF1a.