It is reasonable to initiate ACE inhibitors or ARBs postoperatively and to continue them indefinitely in all CABG patients who were not receiving them preoperatively and are considered to be at low risk (ie, those with a normal LVEF in whom cardiovas- cular risk factors are well controlled), unless contra- indicated.622,627 630 (Level of Evidence: B) Class IIb 1. The safety of the preoperative administration of ACE inhibitors or ARBs in patients on chronic therapy is uncertain.631 636 (Level of Evidence: B) 2. The safety of initiating ACE inhibitors or ARBs before hospital discharge is not well estab- lished.622,628,630,640 (Level of Evidence: B) See Online Data Supplements 26 and 27 for additional data on ACE inhibitors. ACE inhibitors and ARBs are known to exert cardiovasculo- protective actions, particularly in subjects with LV systolic dysfunction, hypertension, diabetes mellitus, or chronic renal insufficiency.626 Nonetheless, the safety and effectiveness of preoperative ACE inhibitors and ARBs in patients undergoing cardiac or noncardiac surgery is uncertain638 because their administration has been associated with intraoperative hypoten- sion as well as a blunted response to pressors and inotropic agents after induction of anesthesia. Of particular concern during cardiac surgery is their reported association with severe hypo- tension after CPB (so-called vasoplegia syndrome) and postop- erative renal dysfunction.631,639 Although it has been postulated that these agents may protect against the development of postoperative AF, published studies have reached conflicting conclusions in this regard.634,636 The safety and efficacy of ACE inhibitors and ARBs after CABG in previously na ve low- to moderate-risk patients (ie, subjects without diabetes mellitus or renal insufficiency and with or Hillis et al 2011 ACCF/AHA CABG Guideline e681 without asymptomatic moderate LV systolic dysfunction) are uncertain; furthermore, ACE inhibitors and ARBs must be used with caution in these subjects. 