Ventricular function and hemodynamic parameters before and after Fontan operation were studied in patients with univentricular heart (UVH) of left ventricular (LV) type (9 cases, ages: 6-66, mean 13 years) and right ventricular (RV) type (13 cases, ages: 6-17, mean 9 years) without atrioventricular valve regurgitation. The preoperative ejection fraction (EF) was poor and only 44% of LV type and 23% of RV type met the Choussat's criterion (EF greater than or equal to 60%). There were 2 hospital deaths each in LV type and in RV type, but their causes could not be attributed to preoperative parameters of ventricular function. In survivors, the EF reduced from 62.9 +/- 7.0% before Fontan procedure to 43.4 +/- 12.6% after the procedure in LV type (p less than .05) and from 54.5 +/- 7.0% to 47.0 +/- 9.0% in RV type (p less than .01), although the ventricular end-diastolic pressure (EDP) also reduced from 12.7 +/- 2.7 mmHg before to 6.6 +/- 1.9 mmHg after the operation in LV type (p less than .05) and 10.4 +/- 2.6 mmHg to 5.5 +/- 2.4 mmHg in RV type (p less than .05). the ventricular end-diastolic volume (EDV) also reduced from 185 +/- 35% to 126 +/- 58% of expected normal volume in LV type (p less than .05) and 173 +/- 28% to 99 +/- 18% of expected normal volume in RV type (p less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)