BACKGROUND : Multi-vessel coronary artery disease (CAD) is associated with worse outcome in non-ST segment elevation myocardial infarction (NSTEMI) patients. Depending on the severity of CAD, there may be prolongation of atrial depolarization time as a result of left ventricular dysfunction and atrial ischemia. Therefore, we aimed to study whether the severity of CAD can be predicted with the P wave peak time (PWPT) in the electrocardiography (ECG) obtained during the diagnosis in NSTEMI patients. METHODS : A total of 162 patients were included. The coronary angiography records of all patients were analyzed and SYNTAX scores were calculated. Patients were divided into two groups, according to CAD severity. In addition to well-known P wave parameters, PWPT, defined as the time from the beginning of the P wave to its peak, was measured in the leads DII and V1. RESULTS : The PWPTs in the leads DII and V1 were significantly longer in the group with severe CAD (71 ± 13 vs. 61 ± 12, p < 0.001, 63 ± 24 vs. 53 ± 18, p = 0.024, respectively). PWPT was found to be an independent predictor of severe CAD and the best cut-off value of PWPT in the lead DII was 69.6 ms with sensitivity of 58.3% and specificity of 78.9%. CONCLUSIONS : Our findings show that prolonged PWPT, which is a parameter easily obtainable from the ECG, is associated with severe CAD. Recognition of NSTEMI patients with severe CAD at the time of diagnosis before performing coronary angiography may be important for the planning of treatment.