Background:There is a concern that clinical outcome of tricuspid valve replacement (TVR) is inferior compared with tricuspid annuloplasty (TAP). The aim of this study was therefore to compare changes in right ventricular (RV) volume and function following TAP with that following TVR on cardiac magnetic resonance imaging (CMR) in patients with severe functional tricuspid regurgitation (TR).Methods and Results:Forty patients who underwent surgery for severe functional TR and who underwent CMR preoperatively and on postoperative follow-up (24.8±13.3 months after surgery) were enrolled. Thirteen patients underwent TAP (TAP group) and 27 patients underwent TVR (TVR group). Both RV end-diastolic and end-systolic volume indices decreased significantly after surgery (from 178.9±53.9 to 116.3±26.7 ml/m², P<0.001, and from 95.7±36.1 to 67.3±28.0 ml/m², P<0.001, respectively), without intergroup differences. In the TAP group, RV ejection fraction (EF) was preserved following surgery (from 43.3±9.5 to 46.9±10.9%, P=0.312). In the TVR group, however, it decreased significantly following surgery (from 51.8±9.2 to 42.4±12.3%, P<0.001). In addition, postoperative RVEF was lower in the TVR than TAP group, with a marginal significance (mean difference, –6.967; 95% confidence interval: –14.529 to 0.595; P=0.070).Conclusions:For patients with severe functional TR, both TAP and TVR are beneficial for reduction of RV volume indices. TAP, however, might be superior to TVR, because RVEF is well preserved following surgery. (Circ J 2016; 80: 1142–1147)