Effects of three unmodified hemoglobin solutions on myocardial contractile function was evaluated using isolated perfused rabbit interventricular septa. The hemoglobin solutions tested were: a human hemoglobin solution (SFHS-A), a bovine hemoglobin prepared by a column chromatography (SFHS-B), and a bovine hemoglobin obtained by a ultrafiltration method (SFHS-C). Myocardial effects were assessed by comparing contractile parameters; developed tension (DT), resting tension (RT), and perfusion pressure (PP), measured before (control perfusion with Tyrode buffer) and during hemoglobin perfusion. Further, to examine the effects of hemoglobin solutions on myocardial contractility following a period of impaired flow, septal responses to a 10-minute period of ischemia (stopflow) were also studied. After a 10-minute perfusion with hemoglobin solution, SFHS-C increased DT to 124 +/- 12% (paired t-test, p less than 0.05) without causing a significant increase in RT or PP while SFHS-A and SFHS-B decreased DT to 96 +/- 20% (p greater than 0.05) and to 77 +/- 7% (p less than 0.05), respectively. A significant rise in PP (40-50% above baseline) was also noted with these solutions (p less than 0.05). Similarly, after a 30-minute reperfusion following a 10-minute ischemia, SFHS-C allowed significantly better percentage recovery (95 +/- 3%) than septa perfused with SFHS-A (81 +/- 2%) or SFHS-B (63 +/- 6%) (Student's t-test, p less than 0.05). These results indicate that hemoglobin solution, if properly prepared, does not seem to have acute deleterious effects on contractile function of the isolated heart.