Effects of prolonged consumption of ubiquinone on myocardial injury caused by ischemia and reperfusion were studied in reperfused rat hearts. Wistar rats received lipophylic or hydrophilic forms of ubiquinone for 6-8 weeks with chow or water, respectively. Isolated isovolumic hearts with a constant volume latex balloon in the left ventricular cavity were subjected to total normothermic ischemia (25 min) and subsequent reperfusion (50 min). Time course of ischemic contracture and its level in both groups of ubiquinone treated animals were similar to those in controls. However recovery of left ventricular developed pressure after reperfusion was significantly better in both ubiquinone groups (54-/+9, 65-/+7, and 24-/+4 mm Hg in animals treated with lipophylic and hydrophylic ubiquinone and controls, respectively, p<0.01). As a result the developed pressure and heart rate product reflecting maximal aerobic capacity of the heart was also better restored. Both ubiquinone groups demonstrated absence of increased coronary tone that was characteristic for control animals. Mitochondria isolated from reperfused hearts of ubiquinone treated rats showed better preservation of structure and respiratory control. Rate of succinate-dependent generation of superoxide radicals determined with a spin trap TIRON in mitochondria from hearts of rats treated with hydrophylic ubiquinone (35-/+8 mmol O(2) /min/g) was approximately twice lower (p<0.05) than in control group (74-/+12 mmol O(2) /min/g) while the value in lipophylic ubiquinone group (48-/+9 mmol O(2) /min/g) did not differ significantly from the control. The results evidence that prolonged consumption of water-soluble ubiquinone increases resistance of rat myocardium to injuring action of reperfusion.