The effect of paired pulse stimulation (PPS) and single pulse stimulation (SPS) at different rates on coronary hemodynamics was studied in 16 open chest right heart bypass dogs. Intrinsic rate was controlled either by sinoatrial node crush or formalin injection of the atrioventricular node. Coronary blood flow (CBF) and myocardial oxygen consumption (MVO2) were significantly higher during PPS than during SPS at the same rate (100/min). CBF and MVO2 during SPS (200/min) and PPS (100/min) were comparable. Increase in SPS rate from 60 to 100, 150 and 200/min was associated with increase in CBF and MVO2. Increase in MVO2 during PPS is probably related to increased myocardial contractility and the O2 cost of the ineffective contraction. Increase in MVO2 with SPS at higher rates is probably related to increased contractility associated with the force-frequency relationship and effect of the larger product of arterial pressure and heart rate.