Chest X-ray examination of a 38-years-old female patient, who was diagnosed as having mitral stenosis, revealed cardiac enlargement due to huge left atrium. Cardiothoracic ratio was approximately 0.90. Cardiac enlargement was due to the distortion of cardiac structures by giant left atrium. Giant left atrium can be readily demonstrated by echocardiography. Delaying the operation for mitral valve replacement may lead to fatal outcomes. Optimal timing for operation is important in mitral stenosis.