The object of this study is to describe the long term effects of a dietary supplementation of n-3 fatty acids on functional and biochemical parameters in patients with coronary heart disease undergoing elective percutaneous transluminal angioplasty (PTCA). We will use this clinical model to study the effects of n- 3 polyunsaturated fatty acids (PUFAs) on risk indicators of atherosclerosis: serum lipids, platelet activation, thromboxane and prostacyclin formation, and plasma fibrinolytic activity. We will also study the interaction of long chain n-3 PUFAs, precursors of 3-series eicosanoids, with aspirin, an inhibitor of cyclooxygenase, which is used to prevent restenosis after PTCA. We will conduct a detailed analysis of the effects of n-3 PUFAs on initial steps of platelet activation related to the phospholipases C and A2. We will relate the changes observed in myocardial perfusion to effects of n-3 PUFAs on eicosanoid formation, serum lipids, plasma fibrinolytic activity, membrane phospholipid composition, and related enzyme systems. Our findings in this clinical model should be relevant to increasing the understanding of the effects of n-3 PUFAs in preventing atherosclerotic disorders. Though epidemiologic studies indicate an association, this prospective clinical study is designed to demonstrate a causal relationship between n-3 PUFA ingestion and decreased thromboatheromatous vascular disease, if such relationship exists. The biochemical changes thought to be associated with a preventive action of PUFAs will be monitored. Because of a relatively high rate of restenosis (25-35 percent) within one year post PTCA, this study is feasible.