Description: Background— Patients who undergo tricuspid annuloplasty during left-side heart valve surgery have a poor postoperative clinical outcome. However, preoperative right ventricular (RV) echocardiography parameters that predict adverse events in these patients are poorly understood. Methods and Results— We studied 74 patients (age, 58±10 years; men, 27%) with significant tricuspid regurgitation who consequently underwent tricuspid annuloplasty during left-side heart valve surgery. A total of 26 adverse events (22 heart failures and 4 cardiovascular deaths) occurred during a median follow-up of 26 months. RV midcavity diameter (hazard ratio=2.44; 95% confidence interval=1.48–4.02; P 〈0.01), RV longitudinal dimension (hazard ratio=1.64; 95% confidence interval=1.10–2.45; P =0.02), and tricuspid valve tethering area (hazard ratio=3.25; 95% confidence interval=1.71–6.19; P 〈0.01) were independently associated with adverse events after adjustment for age and New York Heart Association class III/IV. Receiver-operator characteristic curve analysis demonstrated that RV midcavity diameter (area under the curve=0.74; P 〈0.01) and tricuspid valve tethering area (area under the curve=0.70; P =0.04) were most associated with adverse events at the 1-year follow-up. The presence of either a large RV midcavity diameter or tricuspid valve tethering area was predictive of adverse outcome at 1 year after tricuspid annuloplasty. Conclusions— The present study demonstrates that RV geometry dimensions, namely RV midcavity diameter and tricuspid valve tethering area, are important preoperative measures associated with adverse events in patients undergoing tricuspid annuloplasty.