Chronic congestive heart failure (CHF), caused by left ventricular dysfunction (LVD), is a major cause of morbidity and mortality. CHF is the major form of cardiovascular disease that is increasing in prevalence, LVD progresses from an asymptomatic phase to a severe symptomatic phase. Recent clinical trials have proven that angiotensin converting enzyme inhibitor reduced mortality, morbidity, and disease progression in asymptomatic patients with objectively measured LVD. However, available estimates of LVD prevalence are based on symptomatic patients, not on objectively measured ventricular function parameters. The distributions of ventricular function parameters in the United States population are unknown. Since the prevalence of objectively measured asymptomatic LVD is unknown, the total number of patients with LVD who could benefit from medical therapy is also not known. Furthermore, screening techniques to identify persons with treatable asymptomatic LVD have not been evaluated in a population-based setting. The plasma concentration of n-atrial natriuretic peptide (n-ANP) is a marker for the presence of asymptomatic LVD that may be a valuable screening tool for asymptomatic LVD.