This study was aimed to investigate prolongation of P wave dispersion(PWD) in patients with coronary artery disease. Ten patients who were treated PTCA (percutaneous transluminal coronary angioplasty) and 10 healthy people were included in this study as control group. Symptom limited exercise test with modified Bruce protocol was performed on all subjects. In rest, submaximal, maximal exercise and recovery stage, 12 lead electrocardiogram(ECG) were taken. Minimum and maximum P wave duration(P min, P max) were measured and PWD(difference between P max and P min) was calculated. The velocity of ECG was adjusted to 25mm/s. Significant differences were founded between patients and normal controls in P max and PWD. In rest and maximal exercise stage, P max and PWD in patients were greater than in controls, but not in submaximal exercise stage. This study shown that P max and PWD in coronary artery patients at rest and during symptom-limited exercise test is longer than in healthy controls.