Both the AF guidelines by the American Heart Association, American College of Cardiology, and Heart Rhythm Society and the HF guidelines by the American College of Cardiology Foundation and the American Heart Association recommend against the use of ND CCB in patients with HFrEF. The HF guidelines specify to avoid ND CCB in patients with reduced LVEF, but also mention avoiding most calcium channel blockers in general with the possible exception of amlodipine, due to known adverse effects and potential for harm. However, short term use of diltiazem for the acute control of RVR in patients with HFrEF has not been clearly evaluated. Three studies compare the use of BB and ND CCB in the acute treatment of AF RVR. These studies excluded those with severe (New York Heart Association Class IV) or decompensated HF, however, they did not comment on patients with compensated HFrEF. Most of these studies illustrate no difference, but the most recent study reported a success rate (heart rate (HR) <100 bpm within 30 minutes) of 95.8% with intravenous (IV) diltiazem and 46.4% with IV metoprolol (p<0.0001).