NOS1 and atrial fibrillation: An imbalance between atrial nitric oxide (NO) and ROS production has been associated with the new onset of atrial fibrillation (AF); in particular, the activity of atrial ROS-generating enzymes, such as NOX2-containing NADPH oxidases, is independently associated with postoperative AF in patients undergoing cardiac surgery,1,8–10 whereas knockout of the neuronal NOS isoform increases the probability of AF induction in mice.11