42 mild and moderate hypertensive patients treated with Verapamil, Atenolol and Xipamide were studied. Exercise tests (ET) were performed at the onset and after a month of therapy, in order to detect arrhythmias and repolarization change prevalence of ventricular arrhythmias (VA) was 23.7% and 11.9% for supraventricular arrhythmias (SVA). 45.2% of the exercise tests were considered positive, with a significant correlation with maximum pressure peak. Patients with left ventricular hypertrophy (LVH) showed a significant increase in VA and +ET prevalence (42.1% and 63.2%). After treatment, the prevalence for VA registered a slight decrease and an increase for SVA; these differences not being considered significant. +ET showed a significant decrease in all patients, as well as in those with previous LVH (21.4%, 26.3%). Only atenolol produced a significant decrease in the +ET of patients with previous LVH (75% to 12.5%).