Mitral valve prolapse (MVP) is characterized by typical fibromyxomatous changes in the mitral leaflet tissue with superior displacement of one or both leaflets into the left atrium. An echocardiogram is a fundamental study required for the diagnosis of MVP with a flail leaflet and grading of mitral regurgitation (MR) severity. Most patients with MVP have a risk of cardiovascular morbidity and mortality similar to that of the general population, though moderate to severe MR and left ventricular (LV) ejection fraction less than 50% have been postulated to increase the risk of adverse cardiac events. In this case report, we present an isolated flailed P3 scallop of the mitral valve leaflet leading to severe MR and acute congestive heart failure. A 54-year-old African-American male with a medical history of hypertension, hyperlipidemia, and transient ischemic attack, presented to the emergency department (ED) for evaluation of dyspnea on exertion. The patient reported that his dyspnea started one week prior to ED visit and was associated with intermittent chest pain. He also endorsed mild orthopnea and lightheadedness, though he denied any syncopal event. Vital signs were found within normal limits on arrival. He clinically appeared to be volume overloaded which improved quickly with IV furosemide. Transesophageal echocardiogram (TEE) with 3D image acquisition showed significant for hyper-dynamic LV function and evidence of isolated flailed P3 scallop of the mitral valve (MV) leaflet resulting in a severe eccentric, anteriorly directed MR jet. The MV leaflets did not appear thickened, and there was no evidence of mitral or aortic stenosis. Cardiac catheterization showed multivessel disease for which the patient underwent coronary artery bypass grafting and MV repair. This patient presented with new-onset congestive heart failure secondary to severe MR associated with undiagnosed MVP. Commonly, the middle scallop (P2) of the posterior leaflet is more prone to prolapse due to its redundancy and variable thickness with the impact of greater systolic pressure. However, in this case of acute severe MR, we identified an isolated flail of the P3 segment. We believe that this rare TEE finding was associated with a torn chordae or ruptured papillary muscle secondary to ischemic disease as the posteromedial papillary muscle has a single blood supply and is particularly prompted to injury from myocardial infarction.Copyright © 2020, Salas Noain et al.