Zhao et al. (2012) showed elevated HDAC-1 and 5 expression in human PAH lung; treatment with the Class I inhibitor valproic acid inhibited hypoxia-induced PH in rats. In rat models of hypoxia-induced pulmonary hypertension, treatment with Class I HDAC inhibitors MCD-0103 or MS-275 preserved RV function and attenuated RV hypertrophic and pro-fibrotic remodeling; and valproic acid attenuated RV hypertrophy (Cho et al., 2010; Cavasin et al., 2012). Accumulating evidence suggests HDAC inhibitors may also be of benefit in left heart disease (McKinsey, 2012). Here, HDAC9 is linked to pulmonary hypertension.