A 44-year-old male was admitted to our hospital for dyspnea, associated with severe pulmonary hypertension. The patient fell into a shock state on the next day. Hemodynamic measurements revealed high output heart failure with low peripheral vascular resistance. We suspected shoshin beriberi, a fulminant form of cardiac beriberi, by ruling out other common causes of pulmonary hypertension. The rapid recovery after intravenous thiamine administration and the patient's history of improper diet strongly supported the diagnosis. The present case of shoshin beriberi complicating severe pulmonary hypertension shows that history taking is important in elucidating the etiology and selecting the correct treatment.