Fixed-rate pulsatile cardiopulmonary bypass may improve subendocardial perfusion during ventricular fibrillation and has been employed during intermittent aortic cross-clamping. Variable-rate pulsatile left heart bypass that is governed by venous inflow and is asynchronous to the electrical activity of the heart is currently used in clinical practice. To study the effect of fixed-rate pulsation on myocardial metabolism during left heart bypass, six adult pigs underwent alternating periods of pulsatile (PLS) and nonpulsatile (NPLS) centrifugal pump left atrial-to-aortic bypass in randomized block design. Coronary sinus, aortic, and bypass circuit flows were recorded. Oxygen content and lactate concentration of coronary sinus and aortic blood were measured. Pulsatility index and pulse power index during pulsatile bypass were 4.4 and 4.7 (cycles/s)2, respectively. Percent bypass was maximal at a mean pulsation rate of 41.3 and averaged 92.2 and 91.3 for PLS and NPLS, respectively. Myocardial oxygen consumption per minute was reduced 14.3% during NPLS but was unchanged during PLS compared to control (CTRL). Percent lactate extraction was significantly lower than CTRL during NPLS only. Competition for inflow with the ejecting heart appeared to limit circuit pulsation rate and pulse power index. Fixed-rate pulsation is ineffective in reducing myocardial metabolism and should be avoided in left heart bypass.