Objective: The purpose of this study was to evaluate the prognostic properties of the QT/RR relationship in survivors of myocardial infarction with severe left ventricular dysfunction. Design: The QT/RR interval slope was assessed from 24-h electrocardiographic recordings obtained from 241 patients representative of survivors of an acute myocardial infarction with an ejection fraction &#104 35%. During a median follow-up of 752 days, 63 patients died. Results: In a multivariate analysis QT/RR at night-time was an independent predictor of all-cause mortality. A linear all-cause mortality predictor score was calculated from age, ejection fraction, QRS duration and QT/RR night, allowing identification of a high-risk one-third of the patients with a relative risk of death at 4.0. Conclusion: This study demonstrates independent prognostic information of night-time QT/RR dynamics in patients at high risk after myocardial infarction. A linear predictor score calculated from age, ejection fraction, QRS duration and QT/RR night identifies a high-risk one-third of the patients with a 1-year mortality of 36% vs 9% in the remaining patients.