To test whether left ventricular inflow propagation velocity at the pulsed wave Doppler analysis (IPVpw) is a useful noninvasive index of relaxation, 21 patients under coronary angiography for chest pain were included for simultaneous catheter-based and Doppler studies. IPVpw was derived through the application of range ambiguity, and the time constant of isovolumic left ventricular pressure decline (τ) was acquired by a previously described method. At baseline status, IPVpw correlated significantly with the peak negative dP/dt and τ (r = −0.609, P = .003), but not with the peak velocity of transmitral early flow (E) wave. Sublingual application of nitroglycerin increased heart rate, decreased the transmitral E velocity and transmitral E-to-A velocity ratio, and prolonged the deceleration time of the transmitral E wave. However, there was no significant impact on IPVpw, peak negative dP/dt, or τ. IPVpw correlated with τ (r = −0.533, P < .001) at the combined analysis of the data before and after nitroglycerin application. In conclusion, IPVpw is a preload-independent, noninvasive index of left ventricular relaxation.