Pimobendan, a novel cardiotonic vasodilator, was introduced in Japan for the treatment of acute and mild to moderate chronic heart failure. It is a phosphodiesterase Ⅲ inhibitor and is able to enhance sensitization of myocardial contractile regulatory protein to calcium ions. The combination of these effects contribute to its inotropic activity. In patients with severe congestive heart failure, orally administered pimobendan improves cardiac index, stroke volume index, pulmonary wedge pressure, and systemic and pulmonary vascular resistance. Pimobendan is reported to be well tolerated and largely devoid of the proarrhythmic effects of classical phosphodiesterase Ill inhibitors. Studies also suggested that combination of the inotropic agent pimobendan with an ACE inhibitor such as enalapril may be superior to monotherapy for heart failure patients.