Background: Thiamine-responsive acute pulmonary hypertension of early infancy (TRAPHEI) is a rare but reversible cause of pulmonary hypertension in exclusively breastfed infants of thiamine-deficient mothers.

Case Description: A 2-month-old male infant presented with hurried breathing and excessive crying. Examination revealed tachycardia and hepatomegaly. Echocardiography showed dilated right atrium and ventricle with mild pulmonary arterial hypertension. Routine investigations were normal, and sepsis was ruled out. The infant showed rapid clinical improvement following thiamine supplementation.