["Outcome after correction of atrioventricular septal defect depends to a great deal on the postoperative function of the left atrioventricular valve. The related role of the zone of apposition ('cleft') has been debated: should it be closed (bileaflet repair) or should it be left untouched (trileaflet repair)? This study aims to answer the question by comparing the outcome of patients treated according to these two approaches.", "We reviewed all our patients who underwent repair of complete atrioventricular septal defect from 1984 to 1997 and selected those in whom the closure of the zone of apposition in principle would have been possible. Two groups with similar characteristics were constituted: group I (n=63), where the zone of apposition was deliberately not closed as part of a trileaflet repair (postoperative open zone of apposition) and group II (n=96), where it was electively closed as part of a bileaflet AV valve repair (closed zone of apposition). Since we changed from a trileaflet to a bileaflet repair in 1987, the two groups differ in terms of size and length of follow-up. Outcome was compared with regard to survival and freedom from reoperation for left atrioventricular valve incompetence. Late atrioventricular valve function was evaluated by Echo-Doppler. For statistical analysis, we used Chi-square or Fisher's exact test, the Mann-Whitney test and the log-rank test for comparison of Kaplan-Meier curves. The difference was considered statistically significant with a P-value of 0.05 or less.", 'Early mortality was 9.5% (6/63) in group I and 3.1% (3/96) in group II (P=0.16). Actuarial survival after 1, 4 and 8 years was 80.4, 68.4 and 64.8%, respectively, for group I. Actuarial survival for group II was 94.7, 92.1 and 92.1% (P=0.0002). Freedom from reoperation for left atrioventricular valve regurgitation was 90.2, 85.6 and 77.8% for group I at the same time interval. It was a constant 97.9% for group II (P=0.0016). At reoperation, left atrioventricular valve regurgitation was present through the open zone of apposition in 63% of group I cases. The follow-up is 96% (126/131) complete. An increase in degree of left atrioventricular valve incompetence was noted in 28% (11/39) of group I cases and in 9% (8/87) of group II cases (P=0.0131).'] Does closure of the zone of apposition at correction of complete atrioventricular septal defect improve outcome?