NOS2 and atrial fibrillation: This was demonstrated using a goat model of AF over the course of 6 months.32 In this case, production of [O2−] by NOX was shown to be increased in the left atrium after 2 weeks of AF, whereas at the 6-month time-point, the main sources of increased [O2−] production were the mitochondria and uncoupled NOS.