BACKGROUND: There are very limited published studies in Nigeria on the use of 24 hour Holter electrocardiogram (Holter ECG) in the arrhythmic evaluation of hypertensive and diabetic patients. OBJECTIVE: To evaluate indications, arrhythmic pattern of Holter ECG, and heart rate variability (HRV) among patients with hypertensive heart disease (HHD) with or without heart failure and type 2 diabetes mellitus (T2DM) seen in our cardiac care unit. METHODS: Seventy-nine patients (32 males and 47 females) were studied consecutively over a year using Schiller type (MT-101) Holter ECG machine. RESULTS: Out of the 79 patients, 17 (21.5%) had HHD without heart failure, 33 (41.8%) had HHD with hypertensive heart failure (HHF), while 29 (36.7%) were T2DM patients. The mean (standard deviation) ages of HHD without heart failure, HHF and T2DM patients were 59.65 (+/-14.38), 65.15 (+/-14.30), and 54.66 (+/-8.88) respectively. The commonest indication for Holter ECG was palpitation (38%), followed by syncope (20.3%). Premature ventricular contraction was the commonest arrhythmic pattern among the 79 patients, especially among HHF patients. The HRV using standard deviation of all normal-normal intervals was significantly reduced in T2DM patients (81.03+/-26.33, confidence interval [CI] =71.02-91.05) compared to the HHD without heart failure (119.65+/-29.86, CI =104.30-135.00) and HHF (107.03+/-62.50, CI =84.00-129.19). There was a negative correlation between the duration of T2DM and HRV (r=-0.613). CONCLUSION: Palpitation was the commonest Holter ECG indication and premature ventricular contractions were the commonest arrhythmic pattern among our patients. HRV was reduced in T2DM patients compared with hypertensive patients.