To measure QT interval and QT dispersion, and to evaluate possible relationships between these measurements, heart rate variability parameters, and early myocardial involvement in patients with systemic sclerosis (SSc).Prospective study.Tertiary care centre, University 'La Sapienza', Rome, Italy.Thirty-eight patients with SSc (35 females and three males, mean age 47 +/- 11 years), 19 patients with the diffuse form of disease and 19 with the limited form, and 17 healthy controls (11 females and six males, mean age 43 +/- 10 years) were studied.Both patients and control subjects underwent resting 12-lead electrocardiogram and 24-hour Holter monitoring. Moreover, resting myocardial scintigraphy with 99 m Tc-sestamibi was performed in all SSc patients.Bazett's formula was used to obtain rate corrected value of QT interval (QTc). QT and QTc dispersion were defined as the difference between maximum and minimum QT or QTc interval, respectively. Twenty-four-hour heart rate variability was analysed both in the frequency and in the time domain.Twenty-three SSc patients (60.5%) had myocardial resting perfusion defects (group A) and 15 (39.5%) did not (group B). Maximum QTc interval, QT and QTc dispersion were significantly increased in SSc patients compared to the control subjects. No significant differences between group A and group B were observed for all QT measurements. Furthermore, maximum QTc interval, QT dispersion and QTc dispersion were significantly increased in group A patients compared to the control group. Total power, low-frequency, and high-frequency values were significantly lower in all SSc patients, whether in group A or group B, than in control subjects. On the other hand, low-frequency/high-frequency ratio was similar in all groups. Heart rate variability in time domain analysis showed no statistically significant differences between groups.Patients with SSc have increased QTc interval, QT dispersion, and QTc dispersion. The role of autonomic nervous system and myocardial involvement on ventricular repolarization in patients with SSc needs further investigation.