NPPB and atrial fibrillation: RATAF II is an ongoing Phase 4 trial designed to compare the effects of two rate control drugs in patients with permanent AF, hypothesizing that a 6-month treatment with the NDCC diltiazem will lower the level of NT-pro BNP and increase exercise capacity (peak VO2; volume oxygen) compared to treatment with the beta blocker metoprolol, as low levels of NT-pro BNP are associated with sinus rhythm maintenance.