OBJECTIVES: The aim of this study was to identify which patients with a systemic right ventricle are at risk for clinical events. BACKGROUND: In patients with congenitally or atrially corrected transposition of the great arteries, worsening of the systemic right ventricle is accompanied by clinical events such as clinical heart failure or the occurrence of arrhythmia. METHODS: At baseline, all subjects underwent electrocardiography, echocardiography, cardiopulmonary exercise testing, and cardiovascular magnetic resonance imaging. Clinical events comprised death, vascular events, tricuspid regurgitation requiring surgery, worsening heart failure, and (supra)ventricular arrhythmia. A Cox proportional hazards analysis was used to assess the most valuable determinants of clinical events. RESULTS: A total of 88 patients with a mean age of 33 years were included in the study. Sixty-five percent were men, and 28% had congenitally corrected transposition of the great arteries. During a follow-up period of 4.3 years, 31 patients (35%) experienced 46 clinical events for an annual risk of 12%. Right ventricular end-diastolic volume index measured by means of cardiovascular magnetic resonance imaging or multirow detector computed tomography (hazard ratio: 1.20; p