Biatrial pacing is a promising new therapy for drug refractory AF. This article reports two studies. First, an initial 14-patient experience with a novel technique for biatrial pacing. The authors attempted to pace from the LA vein branches of the proximal CS for LA stimulation. LA vein pacing would potentially offer the advantages of greater interatrial synchronization and possibly greater reduction in AF burden and also of lesser far-field R wave sensing and greater lead stability. Second, a postmortem series examining the number, size, and site of LA veins draining into the proximal CS is described. LA vein pacing was successful in 9 of 14 patients. LA vein electrode parameters have been stable during a median follow-up of 580 days. There were three early lead dislodgments but no other complications. In the second study, a postmortem analysis of 43 human hearts was performed. The study found that 38 (88.4%) of 43 hearts had at least one LA vein draining into the proximal 5 cm of the CS. In addition, 81.2% (33/43) had at least one vein greater than 4 Fr caliber. Thus, pacing in a greater proportion of patients might be achieved by the development and use of smaller (3, 4, and 5 Fr) electrodes. Furthermore, these smaller leads would obviously allow deeper advancement into the LA veins with the potential advantages of greater interatrial synchronization and lead stability and lesser far-field R wave sensing.