The authors report a case of a coronary artery fistula (CAF) after mitral valvuloplasty and a maze procedure. A 73-year-old man was admitted to the hospital with congestive heart failure. He had undergone mitral valvuloplasty and a maze procedure 10 years previously. An abnormal Doppler flow signal in the left atrium was incidentally found on transthoracic echocardiography. It was diagnosed as a CAF on transesophageal echocardiography and other imaging modalities. The detection of the abnormal flow just after the operation suggested a causal relationship between this fistula and the preceding surgical procedure. Acquired CAF following cardiac surgery is a rare abnormality. However, if abnormal flow is found on transthoracic echocardiography after cardiac surgery, this abnormality should be kept in mind.