Cardiovascular beriberi is caused by thiamine deficiency and usually presents as high cardiac output failure associated with predominantly right-sided heart failure and rapid recovery after treatment with thiamine. Because of its rarity in developed countries, the diagnosis can often be delayed and missed. We recently experienced a case of cardiovascular beriberi with pulmonary hypertension which successfully treated with thiamine infusion. A 50-year-old man with chronic heavy alcoholics was refered to our department for dyspnea with mental change. Echocardiography showed marked right ventricular (RV) dilatation and flattening of the interventricular septum with a D-shaped deformation of the left ventricle. Moderate tricuspid valve regurgitation was found and estimated RV systolic pressure was 52 mm Hg. Because of his confused mentality and history of chronic alcohol intake, neurological disorder due to thiamine deficiency was suspected and intravenous thiamine was administered and he continuously received a daily dose of 100 mg of thiamine. Follow up echocardiography showed marked reduction of RV dilatation and improvement of a D-shaped deformation of the left ventricle. He finally diagnosed as cardiovascular beriberi on the basis of dramatic response to intravenous thiamine. Thiamine deficiency can cause reversible pulmonary hypertension, and can still be encountered in the clinical setting. Thus high index of suspicion is critically needed for diagnosis.