Cardiac output, usually expressed as liters of blood ejected by the left ventricle per minute, is a fundamental measure of the adequacy of myocardial function to meet the perfusion needs of tissue at any time. Decreases in cardiac output over time (when cardiac output is measured under similar conditions) may signal myocardial functional deterioration and the onset or progression of heart failure. Conversely, improvements in cardiac output may indicate a positive response to medical therapy. However, most methods for evaluating cardiac output are technically demanding, require specialized training and specialized environments for measurement, and are costly. Therefore, most measurement techniques are impractical for routine evaluation of disease progression and/or response to treatment in the prevention and/or management of heart failure. This paper provides a comparative overview of commonly employed cardiac output measurement strategies with emphasis on developments in impedance cardiography which suggest that impedance cardiography has the potential to make routine assessment and trending of cardiac output a viable alternative to assist in the management of both chronically and acutely ill patients, including those with heart failure. (c)2000 by CHF, Inc.