The characteristic difference in functional tricuspid regurgitation (TR) was studied between acquired valvular heart disease (VHD) and adult atrial septal defect (ASD). Fifty patients of VHD and 20 patients of ASD were subjected to this study. In all patients, the TR volume per beat (VTR) was calculated with our original method using 2-dimensional color Doppler (2-DD) and continuous-wave Doppler (CW) echocardiographies. VTR is obtained by the product of the cross-sectional areas (S) of the base of regurgitant jet in 2-DD and the regurgitant volume of one unit area (Vu) in CW (VTR = 1/3.S.Vu). The preoperative evaluation of TR according to VTR showed a good relationship with the operative findings, and the patients with preoperative VTR greater than or equal to 10 cc were candidates for tricuspid valve repair. In all patients with preoperative VTR less than 10 cc (18 patients of VHD and 10 patients of ASD), VTR decreased postoperatively without any tricuspid valve repair. In patients with VTR = 10-20 cc (19 patients of VHD and 5 of ASD), VTR showed a decrease to below 10 cc after tricuspid annuloplasty (TAP) by Kay's method in 18 patients of VHD and 5 of ASD, and with no tricuspid valve repair in one patient of VHD. In patients with VTR greater than or equal to 20 cc (13 patients of VHD and 5 of ASD), the postoperative VTR diminished to below 10 cc after Kay's TAP in 8 patients of VHD and 5 of ASD, and VTR disappeared after valve replacement (TVR) in 2 patients of VHD.(ABSTRACT TRUNCATED AT 250 WORDS)