The pathogenesis of aortocoronary vein-graft occlusion appears to be similar to the development of atherosclerosis, except that it is more accelerated, especially during the first postoperative year. Initiation of platelet-inhibitor therapy before operation is important especially in patients at high risk of bypass graft occlusion because platelet deposition starts during operation and initiates the process of occlusion. The largest and only placebo-controlled trial to start therapy before operation showed that dipyridamole (Persantine) plus aspirin markedly reduced occlusion (compared with placebo) in both high- and low-risk subgroups both early and at a median of 1 year after operation. Arterial balloon angioplasty often causes severe arterial wall injury, which is a potent stimulus for immediate platelet-thrombus deposition and is probably the main contributing factor in the process of restenosis. Animal studies suggest the potential value of antithrombotic therapy starting the day before the angioplasty procedure, but results from placebo-controlled trials in humans are needed before optimal therapy can be established.