Simultaneous, high-fidelity pressure recordings were obtained from the left and right ventricles of anesthetized dogs. Abrupt elevation of left ventricular pressure produced an immediate rise in right ventricular systolic pressure, while mechanical asynchrony of the two ventricles, induced by endocardial pacing of either ventricle, identified discrete pressure transients in the right ventricular pressure pulse which occurred coincident with peak left ventricular dP/dt. During normal conduction, peak right ventricular dP/dt regularly occurred after pulmonic valve opening and simultaneously with peak left ventricular dP/dt. Thus, the rising portion of the right ventricular pressure pulse is an impure signal, influenced directly by the amplitude and timing of left ventricular isovolumic pressure. These observations suggest that right ventricular pumping function is aided by an in series left ventricle.