We investigated the effect of bovine polymerized hemoglobin-based oxygen carrying (HBOC) solution on myocardial oxygen consumption (MVO2) and substrate use. At 15 min after the end of HBOC infusion (20% blood volume, i.v.) in nine permanently instrumented conscious dogs, mean arterial pressure and coronary blood flow were both increased by 41+/-5% and 93+/-20% (p<0.01) without affecting late diastolic coronary resistance and left ventricular dP/dtmax. Administration of HBOC did not affect arterial PO2 or O2 content, but significantly decreased coronary sinus PO2 and O2 content by 21+/-3% and 36+/-3%, respectively. MVO2 was increased from 7.2+/-0.8 to 15+/-1.8 ml O2/min (p<0.01). Despite an increase in triple product from 44+/-2 to 56+/-3 (p<0.01) 15 min after HBOC, the ratio of MVO2 and triple product was markedly elevated by 62+/-19%. Myocardial free fatty acid consumption was decreased from 14+/-1 to 4.5+/-2.2 microEq/min, whereas consumption of lactate increased from 19+/-6 to 69+/-10 micromol/ min and that of glucose increased from 1.0+/-0.5 to 10+/-3 mg/min (all p values, <0.05). These metabolic changes were not observed in dogs that received angiotensin II at a dose used (20-40 ng/kg/min, i.v.) to match those hemodynamic effects of HBOC. These results suggest that administration of HBOC increases coronary blood flow and MVO2 and shifts cardiac metabolism from using free fatty acid to using lactate and glucose in conscious dogs at rest. These metabolic changes are independent of the HBOC-induced change in hemodynamics.