Cardiac myxoma is a benign primary cardiac tumor. Herein, we report a case of mitral regurgitation due to annular dilatation caused by giant left atrial myxoma. The transthoracic echocardiogram performed in a 65-year-old man who suffered from worsening exertional dyspnea detected a large mass of 81 × 31 mm in the left atrium, causing functional severe mitral stenosis. Radical mass resection was performed. After removal of the aortic clamp, an intraoperative transesophageal echocardiogram revealed moderate mitral regurgitation due to annulus dilatation. Mitral annuloplasty was performed, and mitral regurgitation was controlled. The mass was diagnosed as myxoma histologically. A large myxoma that affects mitral annulus dilatation is rarely reported. Mitral regurgitation may be masked by the presence of a large myxoma. Therefore, it should be carefully evaluated after resection, and mitral annuloplasty should be considered in the presence of significant mitral regurgitation due to mechanical annulus dilatation caused by myxoma.
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