Postoperative left ventricular (LV) time-activity curve and the first derivative in radionuclide method were evaluated in 28 patients with aortic regurgitation to clarify the postoperative cardiac function and to determine the adequate timing of operation. Twenty-eight patients were divided into two groups by preoperative echocardiogram. In Group I cases, echo-finding showed LV contractile dysfunction associated with both enlarged LV end-systolic dimension (LVDs) over 5 cm and depressed fractional shortening (%FS) below 25%. In Group II cases, the finding showed compensated cardiac function with relatively small LVDs below 5 cm or not so depressed %FS over 25%. Preoperative diastolic parameter of LV peak filling rate (PFR) in Groups II of 22 cases was depressed in comparison of normal control, although systolic parameters of peak ejection rate (PER) or ejection fraction were mildly depressed. Postoperatively, those parameters of PFR and PER were improved to normal control level (1. PFR: pre op = 206 +/- 73----post op = 311 +/- 79, p less than 0.001 2. PER: pre op = 309 +/- 65----post op = 389 +/- 103 %EDV/sec. p less than 0.001). In contrast, the preoperative parameters of PFR and PER in Group I of 6 cases were strikingly impaired, and post-operative those parameters were not improved to normal level (1. PFR: op = 154 +/- 39----post op = 190 +/- 88 2. PER: pre op = 223 +/- 74----post op = 244 +/- 78 %EDV/sec, NS). No postoperative complications occurred in Group II cases, in contrast, 2 cases in Group I were complicated with low output syndrome or ventricular fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)