More effective surgical treatment of secondary tricuspid regurgitation was investigated on the basis of intraoperative assessment of tricuspid regurgitation (TR) and clinicopathological study of right ventricular muscle biopsy. From March 1986 to February 1989, more aggressive narrowing of tricuspid valve ring using DeVega's method was performed on 29 patients. They were 8 men and 21 women, with the age of 28 to 71 (mean 53.5). Tricuspid annular diameter before procedure ranged from 31 to 45 mm in size, with the mean of 36.9 mm. Tricuspid annuli were constricted to 27 mm in 20 patients, and to 25 mm in 9 patients. Intraoperative evaluation of TR was done by digital examination from right atrium, contrast echocardiography, and filling regurgitation test on arrested or rebeating heart. But these intraoperative assessment of regurgitation did not predict postoperative residual tricuspid regurgitation. There was no early mortality. Postoperative residual tricuspid regurgitation was observed in only two patients (8.7%) of total cases within a follow-up period of 12 months. Quantitative study of extent of diffuse interstitial fibrosis of the right ventricular wall and diameter of right ventricular myocardial cells obtained by open transmural biopsy were done. The degree of diffuse interstitial fibrosis was assessed by the point-counting method, and mean percentage fibrosis (%fibrosis) was noted as 27.9%. Mean diameter of right ventricular myocardial cells was 19.5 microns in size. The diameter of right ventricular myocardial cell was correlated with pulmonary arterial pressure (r = 0.56).(ABSTRACT TRUNCATED AT 250 WORDS)