Background :The pathophysiology of coronary artery ectasia is not fully understood objective: this study aimed to evaluate the role of platelet aggregability in the pathophysiology of coronary artery ectasia methods: 40 patients of coronary artery disease were grouped into; group 1 twenty (20) patients of coronary artery ectasia (CAE) and group 2 twenty (20) patients of obstructive coronary artery disease without ectasia. Platelet aggregation tests (including ristocetin, collagen, and ADP) whole blood viscosity (using a cone-plate viscometer), D dimer, plasma fibrinogen, INR, complete blood picture, echo Doppler and diagnostic coronary angiographic assessments were done for the two groups. Our results showed: Significantly lower frequency of diabetes mellitus significantly higher frequency of male gender and smokers, significantly higher D dimer level, platelet aggregability parameters, higher TIMI frame counts, mean vessel diameter, and angiographically visible intracoronary thrombi in patients with CAE than those without (P = 0.013, 0.017, 0.004, 0.037, <0.05, <0.05, <0.001, <0.05). Respectively. Platelets aggregability was a powerful independent predictor of anginal pain. We recommend highlighting the beneficial value of the antiplatelet therapy in patients with coronary artery ecstasia .