Ventricular function was evaluated in 18 patients prior to left ventriculography and selective coronary arteriography. Simultaneous left ventricular pressure (catheter-tip manometer) and dP/dt were recorded at resting heart rates and during tachycardia induced by right atrial pacing. Pressure-velocity curves were constructed from which Vmaxand maximum measured contractile element velocity (max VCE) were obtained. Vmaxand max VCEinitially increased with pacing-induced tachycardia in 17 of the 18 patients. Eight patients developed evidence of myocardial ischemia during atrial pacing. During the period of myocardial ischemia there was a decrease in Vmaxand max VCEin all eight patients despite constant or increasing heart rate. In the 10 patients who did not develop evidence of myocardial ischemia with pacing-induced tachycardia, Vmaxand max VCEcontinued to increase or remained constant with increasing rate. Peak left ventricular dP/dt increased coincident with the onset of myocardial ischemia in six of eight patients despite a fall in Vmaxand max VCEin all eight patients during the ischemic period. A highly significant difference was demonstrated between Vmaxvalues of patients with normal ejection fractions and patients with low ejection fractions, both at rest and during pacing-induced tachycardia.