Because beta blockers have been shown to reduce the inci- dence of postoperative AF in CABG patients who are receiving them preoperatively604,605,608 (Section 5.2.5), the STS and AHA recommend that they be administered preoperatively to all patients without contraindications and then be continued post- operatively.618,619 Despite this recommendation, uncertainty ex- ists about their efficacy in subjects not receiving them preoper- atively; in this patient population, their use appears to lengthen hospital stay and not to reduce the incidence of postoperative AF.604,607 Their efficacy in preventing or treating perioperative myocardial ischemia is supported by the results of observational studies and small RCTs.612 614 Although a meta-analysis of available data did not show an improvement in outcomes with perioperative beta blockers,615 observational analyses suggest that preoperative beta-blocker use is associated with a reduction in perioperative deaths.609 611 Another analysis of data from 629 877 patients reported a mortality rate of 2.8% in those receiving beta blockers versus 3.4% in those not receiving Few data are available on the pharmacokinetic disposition of beta blockers in the early postoperative period, when an alteration in gastrointestinal perfusion may adversely affect their absorption after oral administration. An RCT demon- strated a significant reduction in the incidence of postopera- tive AF when a continuous intravenous infusion of meto- prolol was used rather than oral administration.616 The efficacy of beta-blocker use in CABG patients after hospital discharge is uncertain, as data from 2 RCTs and 1 large detailed observational analysis suggest that they exert no benefit over 2 years postoperatively.621 623 In contrast, some observa- tional analyses have reported that they are, in fact, efficacious in high-risk subgroups (eg, those with perioperative myocardial ischemia or elderly subjects with heart failure).624 A contempo- rary analysis of prescription data from 3,102 Canadian patients, 83% of whom were prescribed a beta blocker at the time of discharge, reported that those receiving beta blockers had a reduced mortality rate during a mean follow-up of 75 months.625 Of note, improved survival was noted in all patient subgroups receiving beta blockers, even including those without perioper- ative myocardial ischemia or heart failure. 