Intravenous positive inotropic agents are commonly used to treat the patients with acute decompensated heart failure due to left ventricular systolic dysfunction. Although these agents seem to be beneficial for improving symptoms of heart failure in the short-term; it has been reported that they are associated with increased mortality and morbidity. Levosimendan is a new calcium sensitizer and K-ATP channel opener, has emerged as an alternative option of pharmacologic inotropic support in patients with decompensated heart failure. Recent reports on levosimendan's use in severe heart failure demonstrated that this agent is more favorable drug compared with conventional inotropic agents, though its better profile in terms of myocardial efficiency has not been completely understood. This review summarizes the evidence from current scientific literature including our recent trials regarding the mechanism of action, efficiency and the use of levosimendan.