Objective: We aimed to investigate the effects of autonomic and left ventricular functional and structural changes on QT interval and dispersion differences between normal and prehypertensive patients. Materials and Methods: A total of 291 normotensive patients (<140/90 mmHg) (135 males, age range: 16-75 years, mean age: 45±11 years; 156 females, age range: 17-71 years, mean age 38±10 years) were enrolled into this cross-sectional case-controlled study. Patients were categorized into two groups according to their blood pressure (BP) levels as Group 1 - patients with normal BP (<120/80 mmHg) or Group 2 - patients with prehypertensive BP (120-139/80-89 mmHg). We evaluated autonomic states by using heart rate variability measurements. Left ventricular structure and functions were evaluated by using Doppler echocardiography in both normal and prehypertensive BP groups regarding their effect on QT intervals and QT dispersion. Statistical analyses (Student’s t and Mann-Whitney U tests) were used to evaluate the differences in QT intervals and QT dispersion between the BP groups. Results: There were statistically significant differences between the two BP groups with respect to QT intervals and QT dispersion (for QT min, p<0.001, QTc min, p<0.001 and QT dispersion, p<0.001). We also detected that prehypertensive patients had increased sympathetic activity and slightly impaired left ventricular systolic and diastolic function (for low frequency power / high frequency power ratio -p=0.029, left ventricular ejection fraction - p=0.054, and transmitral peak A wave velocity - p<0.001). Conclusion: QT interval and dispersion differences are present in prehypertension. Moreover, these differences are independent of left ventricular mass. Autonomic changes can be effective on these differences between the patient groups.