Meta-analysis of all six included studies using a fixed-effects model illustrates that carvedilol may effectively reduce the incidence of POAF in adult patients undergoing cardiac surgery. The mechanisms that carvedilol reduces the incidence of POAF are not entirely known. However, there is now an increasing body of evidences that oxidative stress, and inflammation, and increased sympathetic activation are involved in the pathogenesis of POAF. Carvedilol is a b blocker with antioxidant and anti-inflammatory properties, and reduces sympathetic activity. From a pathophysiological point of view, it is plausible that the abovementioned properties of carvedilol might result in the favorable effect on the prevention of POAF. Recently, Khan et al carried out a meta-analysis of randomized controlled trials and confirmed the efficacy of prophylactic betablockers against POAF. Both the Khan meta-analysis and our meta-analysis showed that carvedilol appeared to be more effective than metoprolol for the prevention of POAF. Compared with metoprolol, carvedilol has been shown to increase the levels of antioxidant enzymes. Moreover, carvedilol may 
have direct antiarrhythmic profile through electrophysiological traits, since it blocks multiple cationic channels. These properties of carvedilol, which are not equally shared by metoprolol, may partly explained superior efficacy of carvedilol in preventing POAF. In addition, numerous trials indicate that carvedilol is be er than conventional b1-selective b blockers on reducing sympathetic activation, a risk factor for atrial fibrillation. In this meta-analysis carvedilol did not significantly reduce the LOS. The total incidence of POAF is 26.1%, less than one-third of patients develop POAF and still fewer develop prolonged atrial fibrillation, so the effect of carvedilol on LOS in patients prone to atrial fibrillation would have to be very large to be able to detect an effect of LOS in the total population. In addition, a relatively small number of samples provided available data on LOS, additional studies or data are warranted. One problem with the use of carvedilol to prevent POAF is that the majority of patients does not develop POAF after cardiac surgery but would still be exposed to possible side effects. In this meta-analysis, two trials Loganin reported carvedilol was well tolerated and side effects a ributable to carvedilol were detected. And one trial reported complication rates were similar between carvedilol and control groups, including postoperative myocardial infarction and renal dysfunction. Several potential limitations of this meta-analysis merit consideration. First, our study included only six studies and some of them have a Saikosaponin-C modest sample size. Overestimation of the treatment effect is more likely in smaller studies compared with larger samples. Second, our analysis is based on six clinical studies, and half of them were non-randomized controlled trials. The targeted population, adopted carvedilol protocols, type of control, and study design differed among the included studies. These factors may result in the heterogeneity and have potential impact on our results. Furthermore, these studies lack homogeneity in both the method of postoperative monitoring and in their definition of POAF.