- Non-pregnant adults ≥18 years of age with AF RVR (HR >120 bpm), which will be obtained from vital signs or electrocardiogram, in the emergency department, who have an EF <40% from an echocardiogram within the previous 4 years, and are treated with IV push metoprolol or diltiazem as first line for rate control of AF with RVR. Patients can receive up to two IV push doses but cannot switch treatment medication between these two doses.