The reduction of reperfusion injury by intravenous administration of recombinant human superoxide dismutase (r-hSOD) was evaluated in a dog model. Two hours of left anterior coronary artery clamping were followed by 30 min of partial reperfusion and 30 min of full reperfusion. In the SOD group, r-hSOD (100,000 U/kg) was given intravenously 5 min before reperfusion. Measured left ventricular (LV) segments were classified thermographically by temperature drop into central ( > 2°C) and marginal ( < 2°C) areas. The regional LV functions were evaluated by percentages of both segmental (%SS) and active (%AS) shortening. In the central area, the %SS values after reperfusion were -9% in the control group and -3% in the SOD group (p < 0.05). The respective %AS values were 6 and 29% (p < 0.01). In the marginal area, both groups had %SS values of-3% and respective %AS values of 34 and 22% (all not significant) after reperfusion. In the central area, there was significantly better LV function recovery in the SOD group than in the control group.