BACKGROUND: Congestive heart failure and preserved left ventricular systolic function is a common clinical condition. Although the prognosis in this type of heart failure is better in comparison to systolic dysfunction, prognostic markers to evaluate long-term outcome are lacking. The atrial peptide, N-terminal proatrial natriuretic peptide (proANP), has been shown to predict survival in patients with systolic dysfunction. We intended to evaluate the predictive capability of N-terminal proANP in patients with preserved systolic function (ejection fraction [EF] > or = 0.40). METHODS AND RESULTS: A clinical and echocardiographic examination was performed in 149 patients with idiopathic heart failure from a population-based cohort, and 84 patients were identified to have preserved systolic function, with an EF of 0.40 or greater. The patients were followed up during 7 years with regard to symptoms, treatment, hospitalization, and survival. The patients with normal EFs had greater plasma concentrations of N-terminal proANP compared with a control group, and N-terminal proANP level was an independent predictor of mortality (risk ratio, 2.44; 95% confidence interval, 1.28 to 4.67; P = .007). In addition, a high concentration of N-terminal proANP predicted an increased rate of hospitalization (50% for a level > 1,200 pmol/L versus 19% for a level