HDAC inhibitors, including class I HDAC inhibitor, valproic acid, and class I, II, and IV HDAC inhibitor suberoylanilide hydroxamic acid (vorinostat), have been found to alleviate the growth of established hypoxia-induced PAH in rats and reduce the proliferation of human PASMCs and human PAECs, as well as inflammation in fibroblasts and R-cells [122]. This evidence concerns the gene HDAC9 and pulmonary arterial hypertension.