['The goal of this study was to determine if parasympathetic nerves in the anterior fat pad (FP) can be stimulated at the time of coronary artery bypass surgery (CABG), and if dissection of this FP decreases the incidence of postoperative atrial fibrillation (AF).', 'The human anterior epicardial FP contains parasympathetic ganglia and is often dissected during CABG. Changes in parasympathetic tone influence the incidence of AF.', 'Fifty-five patients undergoing CABG were randomized to anterior FP preservation (group A) or dissection (group B). Nerve stimulation was applied to the FP before and after surgery. Sinus cycle length (CL) was measured during stimulation. The incidence of postoperative AF was recorded.', 'Of the 55 patients enrolled, 26 patients were randomized to group A, and 29 patients were randomized to group B. In all of the 55 patients, the FP was identified before initiating cardiopulmonary bypass by CL prolongation with stimulation (865.5 +/- 147.9 ms vs. 957.9 +/- 155.1 ms, baseline vs. stimulation, p < 0.001). In group A, stimulation at the conclusion of surgery increased sinus CL (801.8 +/- 166.4 ms vs. 890.9 +/- 178.2 ms, baseline vs. stimulation, p < 0.001). In group B, repeat stimulation failed to increase sinus CL (853.6 +/- 201.6 ms vs. 841.4 +/- 198.4 ms, baseline vs. stimulation, p = NS). The incidence of postoperative AF in group A (7%) was significantly less than that in group B (37%) (p < 0.01).'] Does preservation of the anterior fat pad paradoxically decrease the incidence of postoperative atrial fibrillation in humans?