BACKGROUND: Levosimendan (LS) improves cardiac contractility without increasing myocardial oxygen demand. We administrated LS on a monthly intermittent 24-hour protocol and evaluated the clinical effect after 6 months in a randomized, open, prospective study. METHODS AND RESULTS: Fifty patients (age 45-65 years) with LV systolic dysfunction and New York Heart Association (NYHA) III or IV were randomized in 2 groups. LS group (n = 25) was compared with a control group (n = 25) matched for sex, age, and NYHA class. LS was given monthly on a 24-hour intravenous protocol for 6 months. Patients were evaluated by specific activity questionnaire (SAQ) and echocardiography (ECHO) before and 3 to 5 days after last drug administration, whereas 24-hour Holter recording was performed before and during last drug administration. Patients in LS and control group had same baseline SAQ, ECHO, and Holter parameters. At the end of the study, a larger proportion of patients in the levosimendan group reported improvement in symptoms (dyspnea and fatigue) (65% versus 20% in controls, P < .01). After 6 months, the LS group had a significant increase in LV ejection fraction versus controls (28 +/- 7 versus 21 +/- 4 %, P = .003), LV shortening fraction (15 +/- 3 versus 11 +/- 3 %, P = .006) and a decrease in mitral regurgitation (1.5 +/- 0.8 versus 2.7 +/- 0.6, P = .0001). There was no increase in supraventricular or ventricular beats or supraventricular tachycardia and VT episodes in LS group, compared with controls. Two patients from the LS group died in the 6-month follow-up period, compared with 8 patients in the control group (8% versus 32%, P < .05). CONCLUSIONS: A 6-month intermittent LS treatment in patients with decompensated advanced heart failure improved symptoms and LV systolic function.