Cardiopulmonary bypass (CPB) and concomitant cardioplegic arrest (CA) may cause impairment of cardiac function with development of myocardial edema. There are few reports of intraoperative assessment of LV mass or muscle volume (MV) in patients, Fifteen patients (age; 0.5-68), 10 with congenital and 5 with valvular diseases, were studied by epicardial 2-dimensional and M-mode echocardiography. LVMV was obtained from M-mode study at pre- and post-CPB during surgery. Pre and post CPB LVMV-index (ml/m2) and percent change of LVMV were compared. CPB-time was 170 +/- 78 min (mean +/- SD), and CA time was 97 +/- 49 min. LVMV index increased significantly from 89 +/- 35 to 103 +/- 43 ml/m2 after CPB (p less than 0.01). Percent change ranging from -3 to +37% (14 +/- 12) correlated to CPB time (r = .81, p less than .01) and also to CA time (r = .62, p less than .05). These results indicated that CPB with CA caused acute increase in LVMV with a positive relation to its duration.