Background: Acute myocardial infarction patients may be protected against left ventricular thrombus development by mitral regurgitation (MR). This study aimed to assess the incidence of left ventricular thrombosis in patients suffering from acute anterior myocardial infarction and determine if mitral regurgitation prevents the development of left ventricular mural thrombus. Methods: Seventy patients with anterior STEMI were enrolled in this prospective cohort study, they were divided into a non-LV thrombus group (n=55) and LV thrombus group (n=15), 2-dimensional and color Doppler echocardiography were done to all cases. Results: LV thrombus formation was significantly higher among patients presented with passed time anterior STEMI than those presented within 48 hours of chest pain onset (P value < 0.001). LV EDV and LV ESV were significantly higher among LV thrombus group than non-LV thrombus group (P value =0.032). The severity of MR was significantly lower in LV thrombus group compared to the non-LV thrombus group (P value =0.039). Pain to door time was able to significantly predict LV apical thrombus formation (P <0.001 and AUC = 0.875) at cut-off >32 hours with 80% sensitivity, 80% specificity, 52.2% PPV and 93.6% NPV. In Multivariate regression, pain to door time, and severity of MR were independent predictors of LV thrombus formation (P value < 0.05). In univariate regression, ECG, pain to door time, passed time (PCI) and Conservative management, LV EDV, LV ESV and severe grade of MR were independent predictors of LV thrombus formation (with P value <0.05). Conclusion: Pain to door time, and severity of MR were independent predictors of development of LV thrombus while ECG, passed time PCI and Conservative management, LV EDV and LV ESV were not. The associated mitral regurgitation could have a protective role against development of left ventricular mural thrombus following anterior STEMI.