Tricuspid valve regurgitation (TVR) is frequently observed following orthotopic heart transplantation. The etiology of this phenomenon remains unclear. In a prospective study, we tried to identify pre-, intra- and postoperative factors possibly related to the occurrence of TVR in 15 patients (14 male, 1 female). Epicardial echocardiography was used during the transplant procedure and transthoracic echocardiography was performed at weekly intervals thereafter, TVR was graded semiquantitatively (grade 0-4). If TVR grade greater than 1 was detected after discontinuation of cardiopulmonary bypass, pericardial reduction plasty was performed (group R). If no or mild TVR (less than grade 1) was present, simple closure of the pericardium was carried out (control group). In group R the mean grade of TVR was 1.6 +/- 0.3 (SEM) before and 0.6 +/- 0.07 after pericardial closure (p less than 0.05). Following moderate elevation during the first 5 weeks, the degree of TVR reached levels slightly above the initial levels after 8 weeks. In the control group, a moderate increase of TVR developed during the first 8 weeks after surgery and remained at a significantly higher level than in group R (p less than 0.05). No preoperative risk factors for TVR, such as underlying disease or hemodynamic status of the recipients, was identified. Estimation of differences in heart volume between recipient and donor organs, by contrast, showed a significant discrepancy in group R but not in the controls. We therefore conclude that TVR in recipients of orthotopic heart transplants may be due to a size mismatch of donor heart and recipient pericardial cavity, resulting in distortion of the tricuspid valve ring.(ABSTRACT TRUNCATED AT 250 WORDS)