Epidemiologic investigation of the evolution of heart failure in the general population has provided clues to its pathogenesis, predisposing conditions, predictive modifiable risk factors, and indicators of deteriorating ventricular function. It is a major and growing problem because of the increased size of aging populations and the prolongation of the lives of cardiac patients by modern therapy. Susceptible persons must be detected early so that preventive measures can be started because the mortality rate once overt heart failure appears is unacceptably high despite recent innovations in treatment.