The factors which control the performance of the left ventricle include the determinants of myocardial function (preload, afterload, contractility and heart rate) and peripheral vascular function (capacitance and impedance). Arterial pressure represents an interaction of myocardial and vascular factors. When left ventricular function becomes impaired, impedance to left ventricular ejection becomes increasingly important in determining cardiac performance. Increases in impedance may result from the influence on arteries of neural, humoral or structural changes which can occur in response to a fall in cardiac output or an impairment of cardiac reserve. This increased impedance may further reduce cardiac output while myocardial oxygen consumption is increased. Alterations in the peripheral vascular bed therefore probably play an important role in the hemodynamic and metabolic events which usually are attributed to progressive impairment of the heart. Pharmacologie reduction of impedance with vasodilator drugs could become an important adjunct in the management of heart failure of diverse etiologies.