Introduction: Approximately a third of worldwide deaths are caused by ischemic or coronary heart disease, suggesting that greater attention is needed to study the coronary diameter and myocardial vasculature. Material and Methods: In this study, 39 human adult hearts were dissected. The masses of the hearts were measured according to the principle of Scherle and the external diameters of the right coronary artery, the left coronary artery, and the ascending part of the Aorta were measured in millimeters (mm), using a Mitutoyo digital caliper. In the statistical analysis, normal distribution of the variables was assessed using the Kolmogorov-Smirnov test, external diameters were compared using the unpaired Student’s t-test, and Pearson’s correlation was applied to investigate the correlation of the diameters of the left coronary artery and right coronary artery with the Aorta. Significance was set at P <0.05, and the data were analyzed using GraphPad Prism v.5.00 (GraphPad Software, San Diego, CA). Results: The external diameters were as follows: left coronary artery, 5.55±0.16 mm; right coronary artery, 4.38±0.15 mm (P <0.0001); and Aorta, 22.85±0.80 mm. Thus, it was demonstrated that the external diameter of the left coronary artery is 22% larger than that of the right coronary artery, resulting in a greater blood supply via the left coronary artery and a greater passage of atherosclerotic factors. Conclusions: Despite the importance of the coronary arteries for the heart and the body as a whole, few studies correlated morphometric data and possible clinical implications related to coronary artery disea