Acute Coronary Syndrome (ACS) is a major cardiovascular problem causes high hospitalization rates and high mortality rates. NSTEMI is a type ACS, due to the complexity of coronary lesion NSTEMIhas a high mortality rate, so we need to determine the risk stratification when the time is right for revascularization.Electrocardiography (ECG) can detect cardiac abnormalities such as ST-depression or Tinversion to diagnose NSTEMI and can also measure the peak time of the R wave from the ECG. The severity of myocardial infarction obtained from coronary angiography can be calculated using the SYNTAX(SYNergy between percutaneous coronary intervention with TAXus and cardiac surgery)score. This study aims to determine whether there is a relationship between the peak time of the R wave and the SYNTAX score in NSTEMI patient Method: This was a cross-sectional study of 71 patients with NSTEMI who performed angiography at RSUP HAM from July 2021 ato June 2022. R wave peak time and QRS duration were measured on the ECG. The SYNTAX score was calculated based on the angiography results.Statistical analysis was performed to assess the correlation between R peak time and SYNTAX score to measure severity of coronary artery lesion. Result: A total of 71 of NSTEMI patients, which 46 (66.8%) had severe coronary artery lesion (SYNTAX score <23) and 23 (35.2%) had non-severe coronary artery lesion (SYNTAX score ≥23). There was a moderate positive correlation between R wave peak time and SYNTAX score (r=0.449; p<0.001). The R wave peak time can predict the severity of coronary artery diseasefrom results of ROC analysis, with AUC=0.729. Conclusion:From ECG the R wave peak time is correlated with SYNTAX score, which can predict the severity of coronary lesions in NSTEMI patients.