Several factors may influence hemodynamic tolerance of a ventricular tachycardia (VT) episode but, to date, only VT rate has been used as a major detection criterion in selecting implantable cardioverter-defibrillator therapy algorithms. We examined hemodynamic changes during VT in humans and a possible correlation between left and right ventricular hemodynamic indexes. Right ventricular hemodynamic indexes could reflect systemic hemodynamics but previous studies have been inconclusive. Patients with coronary artery disease and a history of recurrent, sustained VT were studied. Aortic pressure and right and left ventricular pressures were simultaneously recorded with 2 dual micromanometer-tipped high-fidelity pressure catheters during sinus rhythm and during induced sustained monomorphic VT. Beat-to-beat analysis was performed using custom-made software. Nine patients (7 men, mean age 60 +/- 8 years, mean ejection fraction 24 +/- 8%) with 11 VT episodes (mean cycle length 283 +/- 48 ms) were studied. During VT, left and right ventricular systolic pressures showed a mean decrease of 57% and 26%, respectively, with weak correlation (r = 0.67, p = 0.06) between both values. There was also an increase in mean left and right ventricular end-diastolic pressures of 26% and 74%, respectively, and no correlation was seen (r = -0.2, p = 0.6). A significant correlation was found between changes in left and right ventricular maximal positive dP/dt (55% and 28% decrease, respectively (r = 0.69, p = 0.03) and between changes in left and right ventricular maximal negative dP/dt (64% vs 39% decrease, r = 0.71, p = 0.02). Most ventricular time parameters in both ventricles differed significantly during VT compared with sinus rhythm; however, only the decrease in right ventricular time to end-diastolic pressure correlated with the decrease in left ventricular systolic pressure, at the 10th VT beat (r = 0.8, p = 0.01). We conclude that left and right ventricles are hemodynamically unequally affected during rapid VT. Although right ventricular pressures cannot be reliably used to assess changes in the hemodynamic status of the left ventricle, additional parameters, such as dP/dt or changes in ventricular time intervals, should be further evaluated for inclusion in implantable cardioverter-defibrillator algorithms.