<p>Shoshin beriberi is an acute, fulminant form of cardiovascular beriberi characterized by hemodynamic deterioration due to thiamine deficiency. Its rarity and non-specific symptoms often make diagnosis challenging. Clinical improvement is rapid after intravenous infusion of thiamine, but some patients with persistent severe myocardial necrosis may be left chronic cardiac insufficiency. We report the case of a 14-year-old boy with a history of malnutrition who developed high-output heart failure, refractory lactic acidosis, and severe myocardial necrosis. Hemodynamics deteriorated rapidly with vasoactive drug support and blood purification therapy. And blood pressure is barely maintained with ECMO support. Hemodynamics reversed rapidly after thiamine administration on day 5 of admission. Because of severe myocardial necrosis, cardiac dysfunction appeared gradually and the patient died of acute respiratory distress syndrome (ARDS) on the 21st day after admission. This case highlights the need for early diagnosis and immediate empirical treatment with intravenous thiamine in patients presenting with unexplained severe metabolic acidosis and circulatory shock. Severe and persistent myocardial necrosis may suggest a poor prognosis.</p>