Background: Despite the presence of several clinical studies evaluating the association of atherosclerosis and MAC, no data is present regarding the value of MAC in predicting CV adverse events in patients with acute coronary syndrome (ACS). Methods: Prospective, observational cohort study including 314 patients presented with ACS and underwent percutaneous coronary intervention (PCI). MAC was defined by increased echodensity located at the junction of the atrioventricular groove and posterior mitral leaflet on the parasternal long-axis, short-axis, or apical four-chamber view. Patients were followed for a median 25.1 (23.1-26.5) months for any occurrence of major adverse cardiovascular events (MACE). Results: Among 316 patients 46 (14%) had MAC. Seventy (22.1%) patients had MACE during the follow-up. Patients with MACE had higher creatinine, white blood cell count (WBC), C-reactive protein (CRP), peak troponin I, glucose level at admission compared to those without MACE. Age (HR = 1.026, 95% CI = 1.004-1.049; p = .023), myocardial blush grade (HR = 0.637, 95% CI = 0.480-0.846; p = .008), MAC (HR = 2.429, 95% CI = 1.126-5.239; p = .026), and WBC at admission (HR = 1.079, 95% CI = 1.007-1.157; p = .031) were independent predictors for MACE. Conclusion: In patients presented with ACS and underwent PCI, MAC detected by TTE was an independent predictor for MACE during the long-term follow-up.