Cardiac myxoma is often discovered as an incidental finding and presents with various subtle symptoms and signs. Electrocardiographic findings are mostly non-specific. Atrial flutter or conduction abnormalities are known to be rare. We report a case of large left atrial myxoma that was diagnosed by transthoracic echocardiography at a primary care clinic. An asymptomatic, 71-year-old woman presented with serial abnormal electrocardiogram changes during a routine consultation. A diagnosis of left atrial myxoma was obtained through transthoracic echocardiography. We report this case with a review of literature on cardiac myxoma associated with arrhythmia.