Inotropic interventions are frequently utilized to augment the performance of the depressed heart. The effects of myocardial ischaemia on the response to two such interventions (heart rate and paired ventricular pacing) were evaluated in 15 isolated perfused isovolumic canine hearts. With normal perfusion pressure, increases in heart rate caused parallel changes in left ventricular pressure (LVP) and dP/dt, while similar increments in heart rate in the ischaemic heart caused LVP and dP/dt to fall. At normal perfusion pressures paired ventricular pacing resulted in stable increments in LVP and dP/dt, but during ischaemic perfusion initial increments in LVP and dP/dt were not maintained. The presence of ischaemia therefore places definite limits on the response of the myocardium to inotropic interventions. The effectiveness of these agents may therefore be severely limited in these circumstances.