Adult onset Still's disease (AOSD) is a multi-systemic inflammatory disorder characterized by several distinguished manifestations including high spiking fever, evanescent salmon-colored skin rash, arthralgia/arthritis, hepato-splenomegaly, lymphadenopathy, sore throat, serositis, and leukocytosis. The frequently noticed cardiopulmonary manifestation is pleuritis, pneumonitis, and pericarditis. Diffuse myocardial dysfunction is uncommon in AOSD, but it may be the cause of life-threatening heart failure. We have experienced a case of AOSD with acute heart failure in 20-year-old female complained of high fever and skin rash. On echocardiogram, the wall motion of left ventricle was globally decreased with a marked diminished ejection fraction (<25%). Two weeks after treatment with high dose steroid and intravenous immunoglobulin, her symptoms and cardiac function on echocardiogram was completely resolved. To our knowledge, this is the first case of AOSD with acute heart failure reported in Korea.