The hemodynamic consequences of atrioventricular (AV) synchrony during ventricular tachycardia were evaluated during cardiac electrophysiologic testing. The relationship between stroke volume and the AV interval was investigated on a beat-by-beat basis in six patients during induced monomorphic ventricular tachycardia. Stroke volume was calculated either (1) in the right ventricle using impedance catheter method (four patients) or (2) in the left ventricle using Doppler measurement of aortic blood velocity (two patients). The impedance catheter method underestimated stroke volume by a factor of 4.2 +/- 2.4 compared with the thermodilution cardiac output method. However, there was a highly linear relationship between both methods for computing stroke volume (r greater than 0.9). Five patients had complete AV dissociation during ventricular tachycardia, and different AV intervals spanned the entire tachycardia cycle lengths. Largest stroke volumes were associated with optimal AV intervals within 120 and 230 msec, resulting in a 97 +/- 59% increase in stroke volume over ventricular tachycardia cycles not associated with atrial activity. Customized atrial pacing during ventricular tachycardia may provide a valuable means for artificially establishing the hemodynamically optimal AV interval and eliminating the ventricular tachycardia cycles not preceded by atrial activity.