We evaluated the acute effect of the application of positive end-expiratory pressure (PEEP) on LV diastolic function in 10 healthy subjects. We assessed load dependent diastolic function by Doppler examination of transmitral flow and load independent diastolic function by color M-mode propagation velocity of early flow into the LV cavity (Vp). During the application of PEEP in comparison to the baseline, we found a significant reduction of the E wave peak velocity [79 (64-83) vs. 65 (57-72) cm/s; p = 0.028] and a significant reduction in Vp [84 (73-97) vs. 53 (48-66); p = 0.012]. Moreover, we found a significant reduction in left atrial area [15 (13-18) vs. 12 (10-14) cm(2); p = 0.018] and right atrial area [12 (11-15) vs. 11 (9-12) cm(2); p = 0.015]. No difference was found in global LV systolic function. The application of PEEP acutely modifies the diastolic flow pattern across the mitral valve, and reduces atrial dimensions.