Pre-diltiazem, Calcium Versus Placebo for Atrial Fibrillation With Rapid Ventricular Response

The goal of this randomized double blind controlled trial is to learn about the effects of calcium when it is given prior to diltiazem for patients with atrial fibrillation ( a type of irregular heart beat) who have rapid ventricular response ( a pulse over 100 beats per minute). Normally diltiazem 0.25mg/kg (max 20mg) is given to slow the heart rate. We will give Placebo versus Calcium Gluconate 2gm given prior to diltiazem. The main questions it aims to answer are: * Does calcium decrease the incidence of low blood pressure (a side effect of diltiazem)? * How does calcium effect the action of diltiazem? Does it interfere with the desired decrease in heart rate? Participants will receive either placebo or calcium immediately prior to the administration of diltiazem. Their blood pressure and pulse will be measured: * prior to study drug administration * post study drug and prior to diltiazem administration * 3 minutes post start of diltiazem * 5 minutes post start of diltiazem * 10 minutes post start of diltiazem * 20 minutes post start of diltiazem * 30 minutes post start of diltiazem Researchers will compare the placebo group to the calcium group to see if there is a difference in the blood pressure and pulse.