Rheumatic mitral valvular heart disease (Rh MVHD) and atrial fibrillation (Af) are closely associated with significant tricuspid regurgitation (TR) before or late after mitral valve replacement (MVR). We sought to elucidate the impact of additive maze operation (MZ) to prevent late TR in this high-risk group. Methods: Data of patients who underwent successful MVR between 1997 and 2004 were reviewed. Clinical and echocardiographic follow-up (FU) durations were 61짹26 and 46짹27 months, respectively. Significant TR was defined as TR grade ���3/4 on comprehensive Doppler study. Results: Among 266 patients (mean age 52짹10 yrs; 62% female), 38 (17%) showed significant TR at FU. The incidence of late significant TR after MVR only, TVP and MZ was 21%, 14% and 5%, respectively (p=.043). In multivariate analysis, female gender (OR=3.72, 95% CI=1.42-9.72), MZ, TVP, and pulmonary hypertension at FU were associated with late significant TR. Among 106 patients with significant pre-MVR TR, the incidence of late TR was 14%; the incidence in MVR only group, TVP and additive MZ group was 50%, 12% and 10%, respectively (p=.024). There was no additive benefit of MZ after MVR and TVP in this subgroup. In the other 160 patients without significant pre-MVR TR, the incidence of late TR was 17%. In this group, additive MZ, not TVP, showed prophylactic benefit (18 vs 4%, p=.022). Conclusions: Additional MZ or TVP is necessary to prevent late TR in patients with Rh MVHD and Af, and preoperative TR severity seems to be useful to select appropriate surgical procedure.