Background: Magnesium is an essential element that plays a crucial role in cardiac and vascular functions. Low levels of intracellular (Mg2+) lead to abnormal vascular cell growth, inflammation, fibrosis resulting in negative vascular remodeling, finally results in CAE. Objective: The aim of this study was to studying serum magnesium level among patients going to do elective coronary angiography for comparing its level in O- CAD patients , and CAE patients , and arelationship between serum magnesium level and CAE . Methods: A case control study was conducted on 84 patients admitted for elective CA for suspected ischemic heart disease. The patients were divided into 4 groups according to CA results. All patients were subjected to detailed history, physical examination, electrocardiography, conventional echocardiography, laboratory investigations and coronary angiography. Results: 84 patients divided into 4 groups, patients with obstructive coronary artery disease (group I), isolated coronary artery ectasia (group II), normal coronaries (group III) and patients with coronary artery ectasia and obstructive coronary artery disease (group IV). A significant correlation was found as regarding serum Mg in between one another group with significant p values, except for comparing group I (obstructive coronary artery disease) with group III (normal coronaries) there was no statistically significant difference in between them with p value 0.984, with best cut-off value considering prediction of CAE >1.8 with 80.95% sensitivity and 71.43% specificity. Conclusion: (Mg2+) level is highly predictive in suspecting the finding of coronary artery ectasia in both obstructive and non-obstructive coronary lesions.