PR interval reflects the slow conduction of an impulse through the AV node, which is controlled by the balance between the sympathetic and parasympathetic divisions of the autonomic nervous system. The objective of the present study was to investigate the mechanism of electrocardiogram's short P-R interval during pregnancy. We included 150 pregnant women for the study, comprising 50 women in each trimester of pregnancy and were compared with another 50 age matched non-pregnant women as controls who had normal P-R interval. ECG was recorded after giving 5 minutes of rest to the subject to allay anxiety in all 12 leads by connecting electrodes to left arm, right arm, left leg and right leg in supine position. The values were expressed as Mean + SD and Z-Test was used for comparison between control and study groups. Categorical data was analyzed by Chi-square test. A 'p' value of less than 0.05 was considered as statistically significant. In first, second and third trimesters of pregnancy, there was highly significant rise in heart rate (p<0.001) as compared to control. There was a statistically significant decrease in PR interval (p<0.001) in all trimesters of pregnancy when compared to control group. This indicates that shortening of PR interval during pregnancy is benign and no treatment is required.