The ECG is a basictool that plays an important role in the definitive diagnosis, predective lesions location, as well as the prognosis and monitoring of patients with acute coronary syndrome( ACS). Value of electrocardiographic T wave inversion in lead aVL for mid-segment left anterior descending (MLAD) lesions in patients with ACShas not been emphasized or well recognized. Objective: To study the relationship between T wave inversion in lead aVL and mid-segment left anterior descending (MLAD) lesions in patients with acute coronary syndrome (ACS). Method: We performed a cross- sectional study include 401 patients with acute coronary syndromefor the first time (214 STEMI, 187 NSTEMI) , who underwent PCI at The Vietnam Heart Institutef-rom August 2020 to August 2021. The primary outcome was MLAD lesion ≥ 70% and MLAD lesion as the culprit. Results: In STEMIgroup,T wave inversion in aVL was found to be the only ECG variable significantly predicting mid segment left anterior descending artery (MLAD) lesions (OR=2,17, CI95% =1,17-3,97, p<0,05) .T wave inversion in lead aVL had a sensitivity of 64,5%; 71,7%, positive predictive value of 78,1%; 50% for predicting MLAD lesions/MLAD lesion as the culprit.Isolated T wave inversion in lead aVL had a specificity of 92,8% for predicting MLAD lesions.In anterior STEMI, T wave inversion in lead aVL had a sensitivity of 70,2%; 71,1%, positive predictive value of 78,5%; 68,8% for predicting MLAD lesions/MLAD lesion as theculprit. In inferior STEMI, this relationship is not significantly different.