Sample size was calculated based on a group sequential test of two proportions (NQuery, Statistical Solutions Ltd., Boston, MA), which takes into account a single interim analysis of SGB efficacy once 50% of the proposed study group have been enrolled. At 80% power, cumulative alpha = 0.05, with a two-sided test with continuity correction, and using the O'Brien-Fleming spending function, a total study group of n=632 (n=316/ treatment group) would be required to detect a decrease in the rate post-operative atrial fibrillation from 30% to 20% with stellate ganglion block. After taking the interim analysis (performed when n=350; significance accepted at p<0.003) into account, significance will be accepted at p<0.047 for the overall study. In our preliminary feasibility study, the investigator established that stellate ganglion block was successful in 88% of cases; thus, the sample size was increased by 12%, from n=632 to n=707.