Abstract(#br)Wet beriberi-induced pericardial effusion has rarely been previously described. Little is known about the effect of beriberi-induced pericardial effusion on hemodynamics. Here we present a case of wet beriberi with pericardial effusion that exhibited constrictive physiology, which was dramatically improved after treatment. A 61-year-old male patient was admitted to our hospital for progressive leg edema, dyspnea on exertion, and lower-extremity muscle weakness. Echocardiography showed a hyperkinetic left ventricle and a moderate amount of pericardial effusion. Hemodynamic measurements, including simultaneous measurement of left and right ventricular pressures, revealed high output heart failure and constrictive physiology. Blood test showed lactic acidosis, and low level of... serum thiamine levels; consistent with a diagnosis of wet beriberi. After thiamine replacement therapy, the patient’s hemodynamic state rapidly improved. Additionally, pericardial effusion decreased and constrictive physiology was successfully resolved. No other possible causes of pericardial effusion could be identified, with the exception of thiamine deficiency. This case illustrates the importance of considering wet beriberi as a possible cause of pericardial effusion with constrictive physiology.