Objectives This study sought to investigate the incidence and identify the predictors of significant tricuspid regurgitation (TR) development long after left-sided valve surgery.Methods Of 615 patients who underwent surgery for left-sided valve disease between 1992 and 1995, 335 patients without significant TR who completed at least 5 years of clinical and echocardiographic follow-up were enrolled. Late significant TR development was assessed by echocardiography with a mean follow-up duration of 11.6 ± 2.1 years.Results Significant late TR was found in 90 patients (26.9%). Patients with late TR showed an advanced age (47.6 ± 13.4 vs 44.3 ± 13.2 years, P = .04), a higher prevalence of preoperative atrial fibrillation (83.3 vs 46.5%, P b .001), a greater left atrial dimension (56.9 ± 13.2 vs 52.4 ± 11.5mm, P = .006), and a higher prevalence of prior valve surgery (40.0 vs 25.3%, P = .01). In addition, late TR occurred more frequently in patients who had undergone mitral valve surgery than in those who did not (93.3 vs 72.2%, P b .001). However, multivariate analysis showed that the presence of preoperative atrial fibrillation (odds ratio 5.37; 95% CI 2.71-10.65; P b .001) was the only independent factor of late TR development. Patients who developed late TR had a lower event-free survival rate than those who did not (P = .03).Conclusions The development of significant TR long after left-sided valve surgery is not uncommon with an estimated incidence of 27% and is closely associated with a poor prognosis. The presence of preoperative atrial fibrillation was identified as the only independent predictor of the development of late TR. (Am Heart J 2008;155:732-7.) Tricuspid regurgitation (TR) is a common finding in patients undergoing mitral or combined mitral/aortic valve surgery. 1,2 Although TR may decrease gradually after left-sided valve surgery owing to reduced right ventricular pressure or volume overload, 3 TR does not always regress after adequate correction of the underlying lesions 4,5 and often progresses some time after surgery without leftsided valvular dysfunction, even after tricuspid annuloplasty. Furthermore, TR can appear de novo during postoperative follow-up. Because it is well known that TR progression badly affects long-term mortality and morbidity, and that surgical correction of TR after left-sided valve surgery is associated with disappointingly high mortality and morbidity, 6-9 the prevention of late TR is clinically important. In this regard, information regarding the incidence and predictors of progression or development of late TR is of substantial value for determining optimal operative timing and the surgical strategy to prevent late TR development, at the time of surgery for underlying left-sided valve disease. Several previous reports on this topic have been limited by a relatively small study population, 5,10 a short-term follow-up, 11 or the lack of reliable echocardiographic data. 12 Therefore, the present study was performed to investigate the incidence of late de novo TR develo...