Adults with tetralogy of Fallot (TOF) have increased long-term mortality. The identification of patients at greater risk for death or cardiac-related morbidity is challenging. This study was conducted to assess the prognostic value of cardiopulmonary exercise testing in adults with repaired TOF. One hundred eighteen consecutive adults with repaired TOF (mean age at repair 4.8 +/- 4.2 years) underwent cardiopulmonary exercise testing at a mean age of 24 +/- 8 years (range 16 to 59). The degree of pulmonary regurgitation, right ventricular function, and right ventricular systolic pressure were determined by transthoracic echocardiography. After the exercise tests, patients were regularly followed up for cardiac-related events. During a mean follow-up of 5.8 +/- 2.3 years (range 0.6 to 9.7), 9 patients died and 18 underwent hospitalization. Peak oxygen uptake (hazard ratio 0.974, 95% confidence interval 0.950 to 0.994), the slope of ventilation (VE) per unit of carbon dioxide production (VCO(2)) (hazard ratio 1.076, 95% confidence interval 1.038 to 1.115), and New York Heart Association functional class (hazard ratio 2.118, 95% confidence interval 1.344 to 3.542) were independent predictors of death or hospitalization. Patients with peak oxygen uptake < or =36% of predicted value and those with VE/VCO(2) slopes >39 were at greater risk for cardiac-related death (5-year mortality 48% vs 0%, p <0.0001, and 31% vs 0%, p <0.0001, respectively). In conclusion, the measurement of peak oxygen uptake and VE/VCO(2) slope in adults with repaired TOF can be prognostically important and could become a powerful tool to rationalize decisions regarding the prevention of premature sudden death and the need for reintervention.