We herein describe a safe and reproducible technique for left atrial volume reduction in patients with a giant left atrium. In a 56-year-old patient undergoing redo mitral valve replacement, the left atrium measured 18 x 20 x 17 cm occupying the middle-lower segment of the right hemithorax with compression of the adjacent organs. The left atrial volume was reduced by triangular resections of the atrial wall and the mitral valve was replaced using a mechanical prosthesis. The postoperative course was uneventful and the left atrial diameter was 11.2 cm at the latest control.