Background: Acute flail mitral valve frequently results in severe mitral regurgitation. However, its clinical presentation can be similar to other disease processes, potentially leading to initial misdiagnosis and a morbid outcome. We sought to analyze baseline characteristics, clinical presentations, time to diagnosis, and in-hospital mortalities of patients with the acute flail mitral valve. Methods: Two hundred and sixty two consecutive echocardiograms with severe mitral regurgitation performed between February 2005 and October 2010 at the Jack D. Weiler Hospital (Bronx, New York, USA) were reviewed. Adult patients who had presented with new onset flail mitral valves were selected for this retrospective study. Results: Fifteen patients were found to have acute flail mitral valve. The majority was elderly male. Over half presented to the emergency room with a sudden onset of dyspnea. A mitral regurgitant murmur was appreciated in only a third of the patients. The chest X-ray of five patients had no acute pulmonary findings, whereas, two were found to have gross unilateral pulmonary edema. Clinically, 60% were misdiagnosed on admission. Using echocardiogram, the correct diagnosis of flail mitral valve was made in all cases, however, only 40% on the day of presentation. The maximum time to echocardiographic diagnosis was 4 days. The main cause of acute flail mitral valve was degenerative disease. Seven patients were managed surgically. Overall, there was only one mortality (7%) during incident hospitalization. Conclusions: Initial misdiagnosis of acute flail mitral valve happens frequently. Early echocardiographic exam is essential in the timely diagnosis and management of acute flail mitral valve.