In all animal models of PAH studies to date, apelin is reduced in the right ventricle in the monocrotaline rat (Falcão-Pires et al., 2009) and Sugen 5416 with hypoxia-induced (Drake et al., 2011; Frump et al., 2015) rat models of PAH. The gene discussed is APLN; the disease is pulmonary arterial hypertension.