HDAC1 and idiopathic pulmonary arterial hypertension: Here, we comprehensively report site specific regulation of class I HDAC isoforms, specifically upregulation of HDAC8 in IPAH-lungs, HDAC1 and HDAC8 in remodeled PAs and HDAC1, HDAC2 and HDAC8 upregulation in PAAFs of IPAH patients.