Secondary tricuspid dilatation may or not be accompanied by tricuspid regurgitation (TR). Tricuspid dilatation can be objectively measured whereas TR can vary according to the preload, afterload, and right ventricular function. The purpose of this prospective study was to determine whether surgical repair of the tricuspid valve based on tricuspid dilatation rather than TR could lead to potential benefits. Between 1989 and 2001, 311 patients underwent mitral valve repair (MVR). The tricuspid valve was examined in each patient. Tricuspid annuloplasty was performed only if the tricuspid annular diameter was greater than twice the normal size (> or = 70 mm) regardless of the grade of regurgitation. Patients in group 1 (163 patients; 52.4%) received MVR alone. Patients in group 2 (148 patients; 47.6%) received MVR plus tricuspid annuloplasty. Although not significant there was a difference with regard to hospital mortality (group 1 = 1.8%, group 2 = 0.7%) and actuarial survival rate (Kaplan-Meier: group 1 = 97.3%, 96.2%, and 85.5%; group 2 = 98.5%, 98.5%, and 90.3% at 3, 5, and 10 years, respectively). The New York Heart Association (NYHA) functional class was significantly improved in group 2 (group 1 = 1.59 +/- 0.84; group 2 = 1.11 +/- 0.31; p1). TR increased by more than two grades in 48% of the patients in group 1 and in only 2% of the patients in group 2 (p < 0.001). Remodeling annuloplasty of the tricuspid valve based on tricuspid dilation improves functional status irrespective of the grade of regurgitation. Considerable tricuspid dilatation can be present even in the absence of substantial TR. Tricuspid dilatation is an ongoing disease process that will, with time, lead to severe TR.