We previously reported that L‐carnitine upregulates lung endothelial Cpt1a expression.[16] Here, we treated hyperoxia‐exposed mice with L‐carnitine (150 and 300 mg kg−1, i.p., daily) between pnd14 and pnd27 and determined pulmonary arterial wall thickness, Fulton index, and pulmonary hypertension at pnd28. The gene discussed is CPT1A; the disease is pulmonary arterial hypertension.