In 14 patients (pts) with aortic valve disease (AVD) left ventricular (LV) relaxation was assessed by the time constant (T) of LV pressure (tipmanometer) fall before and 19 months after successful aortic valve replacement (AVR). 12 control pts (CO) were studied by the same technique. Preoperative LV ejection fraction in AVD (64%) and in CO (69%) did not differ. In AVD T was increased (60 ms) as compared to the CO (38 ms, P less than 0.05). During handgrip (HG) there was a similar increase of LV peak systolic pressure (LVSP), heart rate and peak measured contractile element velocity of shortening in AVD and in the CO. LV end-diastolic pressure varied minimally in both groups. T decreased during handgrip in CO (38 to 33 ms, P less than 0.01) and remained unchanged in AVD. Following AVR T at rest decreased insignificantly to 52 ms, but remained increased (P less than 0.025) as compared with CO. During postoperative HG however, a decrease to 47 ms (P less than 0.05) was noted. Postoperative angiographic LV muscle mass (105 g/m2) and LVSP at rest (137 mmHg) remained elevated (P less than 0.02) as compared to CO (72 g/m2; 119 mmHg). It is concluded that (1) in AVD with normal ejection performance LV relaxation at rest is prolonged and the reaction of relaxation to HG is abnormal despite preserved contractile response, (2) following AVR the response of LV relaxation to HG becomes normal and (3) elevated postoperative T at rest appears to be related to residual hypertrophy and probably also to the still increased LVSP rather than to intrinsic disturbances of myocardial relaxation.