The content of glutathione disulfide (GSSG) in tissue, coronary sinus blood plasma, and in cardiac lymph was measured in a well-characterized model of regional cardiac ischemia and reflow in dogs in vivo in order to assess the magnitude of the oxidant stress produced. No increase in GSSG content was observed during 60 min of occlusion of the circumflex or left anterior descending arteries, or during up to 70 min of reflow. The contents of 11-, 12-, and 15-hydroxyeicosatetraenoates (HETEs) in total lipids also were not increased following 60 min of regional ischemia and up to 60 min of reflow. In addition, global ischemia produced by aortic crossclamping and cardiopulmonary bypass did not increase HETE content. In contrast, infusion of tertiary butyl hydroperoxide (tBHP) into the left atrium produced readily measurable increases in GSSG content with or without prior induction of myocardial ischemia. Infusion of tBHP also increased tissue contents of the HETEs. These findings indicate that the canine myocardium subjected to ischemia-reflow conditions does not generate large amounts of reactive oxygen and does not form significant amounts lipid peroxidation products.