Dietary fish oil has been shown to exert protective effects against arrhythmias and myocardial infarction after coronary artery occlusion. However, the effects of fish oil on ischemia-reperfusion-induced cardiac dysfunction are not known. This study was designed to examine if long-term dietary fish oil protects against a rise in coronary perfusion pressure and myocardial contractile dysfunction following ischemia and reperfusion. Fifteen Sprague-Dawley rats (age 7 to 9 weeks) were fed fish oil-rich chow for 4 to 5 weeks and 11 rats from the same batch were fed ordinary chow. Three fish oil-fed rats were also fed ad libitum indomethacin for the last 2 days. Isolated hearts from both groups were perfused on a Langendorff apparatus and were subjected to 25 minutes of global ischemia and 20 minutes of reperfusion. Myocardial phospholipid acid content was also measured. After 4 to 5 weeks of dietary fish oil supplementation, myocardial content of long-chain polyunsaturated fatty acid (PUFA) (C20-C22) and omega-3 PUFA was increased and that of omega-6 PUFA was decreased in the fish oil-fed group (all p < 0.01). Following global ischemia and reoxygenation, there was a reduction in the force of cardiac contraction and an increase in coronary perfusion pressure. However, reduction in the force of cardiac contraction was less in the hearts of fish oil-fed rats than in the control hearts (49 +/- 9% vs 63 +/- 5%, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)