Increased left ventricular myocardial mass (LVM) is a well known prognostic marker of poor cardiac outcomes. Decreases in LVM have been shown to decrease the cardiovascular risk. Aged garlic extract (AGE) has been shown to have an overall favorable effect on cardiac health; however, to the best of our knowledge, no study to date has specifically examined its effects on left ventricular mass. This study investigated whether AGE can affect LVM measured by cardiac computed tomography angiography (CCTA) in patients with diabetes mellitus (DM). This is a double-blind, placebo controlled randomized trial. In total, 65 participants with DM with a mean age of 58 years were prospectively assigned to consume 2,400 mg AGE/day or the placebo orally. Both groups underwent CCTA at baseline and follow-up at 1 year apart. LVM was measured using automated software. The baseline characteristics did not differ between the AGE and placebo groups. There was a trend towards a significant reduction in LVM at follow-up as compared to baseline in the AGE group (119.30±34.77 vs. 121.0±34.70, P=0.059). No change was observed in LVM in the placebo group at 1-year follow-up as compared to baseline (124.6±37.33 vs. 124.6±35.13, P=0.9). On the whole, this study indicated that AGE may decrease or stabilize LVM. Further studies however, with a larger sample size and longer follow-up times are required to evaluate the effects of AGE on hypertension and LVM.