HDAC9 and cardiac hypertrophy: Among the HDACs, class IIa (HDAC4, 5, 7 and 9) are thought to be cardiac protective because overexpression of HDAC4, HDAC5, or HDAC9 in cardiac myocytes suppresses expression of a pro-hypertrophy transcription factor, Mef2 (myocyte enhancer factor-2), and reduces stress-induced cardiac hypertrophy (34).