A 71-year-old woman was admitted to our institution with symptoms and signs of acute congestive heart failure. The patient had a long history of rheumatic heart disease and, in 1974, she had undergone mitral valve replacement with a single tilting-disk mechanical valve. Transthoracic echocardiography showed a giant left atrium, measuring 18.5 cm longitudinally and 17 cm transversely from the apical four-chamber view with a volume of 1706 ml/m2 body surface area, associated with intense spontaneous echocontrast. Massive tricuspid regurgitation and severe pulmonary hypertension were diagnosed. It could be hypothesized that the giant left atrium may have contributed to the development of acute decompensated heart failure resulting in a significant reduction of left ventricular preload.