Background and Objectives: Atrial fibrillation (AF) is a frequent comorbid condition and aggravating factor of acute heart failure (AHF). However, the impacts of changes of initial AF on clinical outcomes have been poorly studied. Methods: Among 3,200 patients from the Korean Acute Heart Failure Registry, 728 patients with AF at admission were divided into 2 groups; patients with AF at discharge (persistent AF group, n=168, 69.6짹13.6 years) versus patients with sinus rhythm (SR group, n=560, 69.7짹13.1 years). Baseline characteristics and initial clinical outcomes were compared. Results: The rhythm conversion from AF to SR was observed in 560 patients (76.9%). The duration of hospitalization (14.4짹20.5 vs 11.1짹9.3 days, p=0.032) and intensive care unit stay (4.6짹17.0 vs 2.2짹4.2 days, p=0.045) was significantly longer, and the total amount of hospital cost (7.9짹20.3 x 1,000,000 vs 4.4짹5.0 x 1,000,000 won, p=0.042) was significantly higher in persistent AF group than in SR group. The incidence of in-hospital death (9.5% vs 4.5%, p<0.001), in-hospital stroke (4.2% vs 0.5%, p<0.001), or rehospitalization within 1 month after discharge (8.9% vs 3.9%, p=0.002) was significantly higher in persistent AF group than in SR group. Conclusion: The present study demonstrated that lots of patients with AF at admission showed rhythm conversion to SR and the persistence of AF was associated with poor clinical prognosis in Korean patients presented with AHF.