Introduction Diltiazem is commonly used for the management of atrial fibrillation (AFIB) with rapid ventricular rate (RVR) in the emergency department (ED). Conflicting studies comparing the efficacy of diltiazem have led to various dosing strategies. The objective of this study was to investigate diltiazem administration in a community ED and determine the effect of varying doses on heart rate (HR) control, systolic blood pressure (SBP) and diastolic blood pressure (DBP). Methods This is a retrospective, single-center study of adult patients treated with diltiazem for AFIB-RVR in the ED between January 1 and December 31, 2019. Inclusion criteria included pretreatment HR > 120 beats per minute (bpm). Patients were administered diltiazem at the discretion of the ED physician. Primary endpoint was time to achieve HR < 100 bpm after diltiazem. Secondary endpoints included mean weight-based dose of diltiazem, percentage of patients achieving HR < 100 bpm within 240 minutes of diltiazem, nadir SBP and nadir DBP. Results Ninety-nine patients were included in the study. Seventy-two percent of patients received ≤ 10 mg diltiazem bolus. Mean weight-based dose of diltiazem bolus was 0.13 mg/kg. Mean time to achieve HR < 100 bpm was 270 minutes for the entire cohort. Patients treated with ≥ 0.13 mg/kg diltiazem achieved an HR < 100 bpm at a mean time of 169 minutes compared to 318 minutes for < 0.13 mg/kg (p = 0.0107). HR control was achieved in 61% of patients who received ≥ 0.13 mg/kg compared to 36% of patients who received < 0.13 mg/kg diltiazem (p = 0.0213). No patients discontinued diltiazem for hypotension or bradycardia. The lowest recorded SBP and DBP within 240 minutes of diltiazem were 90 mmHg and 47 mmHg, respectively. There was no significant difference in the lowest SBP and DBP for patients who received < 0.13 mg/kg compared to ≥ 0.13 mg/mg diltiazem. Conclusion The majority of patients with AFIB RVR received a 10 mg non-weight-based diltiazem bolus dose in the ED. Diltiazem bolus dosing ≥ 0.13 mg/kg was associated with significantly improved times to achieve HR control compared to < 0.13 mg/kg and was not associated with hypotension or bradycardia.