The incidence and severity of arrhythmias increase during pregnancy. Although the exact mechanism is unknown, increased plasma volume, increased sympathetic activity and hormonal changes were suspected. Estrogen increases excitability in uterine muscles. So it may Show similar effect on myocardial cells by increasing alfa –adrenerjik receptors. P wave dispersion (PWD) a good predictor of atrial fibrillation which was shown in previous studies. P wave dispersion is reflection of heterogeneity of atrial myocardium on surface ECG P waves. The effect of pregnancy on PWD is not known exactly. We aimed to investigate The effect of pregnancy on P wave dispersion in pregnant woman who have not known cardiac diseases. Seventy pregnant (mean age 27 ±3,5 year) and 70 un-pregnant (mean age 30 ± 2,3 year ) were included to study. ECG was obtained from all cases. P wave duration were measured in all leads. The longest P wave duration and shortest P wave duration were defined as P max and P min respectively. P wave dispersion was calculated by the difference between P max and P min. Maximum P wave duration 106 ±15 msn, Minimum P wave duration 64 ± 11 msn and P wave dispersion was 42 ± 4 msn, in pregnant women. Maximum P wave duration 110 ±13 msn, Minimum P wave duration 72 ± 12 msn and P wave dispersion was 38 ± 1 msn, in control group. There was no significant difference between groups. In conclusion the pregnancy is not significant effect on P wave dispersion.