HDAC1 and cardiac hypertrophy: Cardiac tissue-specific deletion of HDAC1 or HDAC2 alone resulted in no effect on the heart, but deletion of both together resulted in cardiac defects.115 Some reports suggested that activity of the class IIa HDACs (HDAC4, 5, 7 and 9) suppress cardiac hypertrophy (heart wall thickening)116 whereas class I enzymes (HDAC1 and 2) promote hypotrophy.117 Knocking out HDAC7 leads to vascular fatalities in mice.118