Previous studies have demonstrated that MPO exerts a potential influence on many cardiovascular diseases, including atherosclerotic plaque rupture, diabetic vasculopathy, myocardial ischemia/reperfusion injury, hypertension, heart failure, pulmonary arterial hypertension, stroke, cardiac arrhythmia, venous thrombosis [6, 7, 16], and chronic kidney disease [17]. Here, MPO is linked to pulmonary arterial hypertension.