When a Cardiac Tumor Mimics Valvular Disease: Giant Left Atrial Myxoma Causing Functional Mitral Stenosis

Cardiac myxomas are the most common primary cardiac tumors and may present with nonspecific manifestations, frequently leading to delayed diagnosis. Large left atrial myxomas can rarely mimic valvular heart disease by causing dynamic obstruction of transmitral flow. We report the case of a 46-year-old previously healthy woman presenting with progressive exertional dyspnea and orthopnea. Transthoracic echocardiography demonstrated a giant left atrial mass measuring 69 × 34 × 31 mm attached to the interatrial septum, prolapsing into the left ventricle during diastole and causing functional mitral stenosis through a dynamic ball-valve mechanism, with a mean transmitral gradient of 9.81 mmHg. Surgical resection was successfully performed, and histopathological examination confirmed atrial myxoma. The postoperative course was uneventful with complete symptom resolution. This case highlights the importance of considering structural intracardiac lesions in patients with unexplained heart failure symptoms and illustrates how giant atrial myxomas may mimic valvular pathology.