To investigate the short-term effects of cilazapril on left ventricular diastolic functions in patients with essential hypertension, 20 patients with mild-to-moderate essential hypertension were evaluated. Following 2 weeks of placebo washout, all patients underwent blood pressure determination and echo-Doppler ultrasonography recordings. Cilazapril, 2.5 mg, was given to all patients, and blood pressure was determined. Echo Doppler ultrasonography recordings were repeated 3 h after drug therapy. The investigated diastolic function parameters were peak and mean velocities of mitral E and A waves, ratio of peak E to peak A, and acceleration and deceleration rates of E and A waves. Both systolic and diastolic blood pressure changes were insignificant. The E wave peak and mean velocities were significantly increased (p = 0.006 and 0.02, respectively), and the A wave peak and mean velocities were significantly reduced (p = 0.006 and 0.02, respectively) after cilazapril therapy. The ratio of peak E to peak A velocity was also found to be increased following cilazapril therapy (p = 0.006). It is to be concluded that the immediate improvement of left ventricular diastolic functions after cilazapril therapy despite the lack of blood pressure decrease is probably a result of the inhibition of tissue angiotensin-converting enzyme and/or other local humoral factors, but this needs to be further investigated.