This is a prospective study. Consecutive patients, who were hospitalized because of acutely decompensated HF due to systolic dysfunction and decided Levosimendan administration, were enrolled. Patients were classified into two as those with AF (group A) and those with sinus rhythm (control group, group S). All patients had echocardiography before and after administration. Echocardiographic data were evaluated by ANOVA repeated measurements test.