A prolonged QT interval is a risk factor for ischemic heart disease in hypertensive subjects. Patients with renal-artery stenosis and primary aldosteronism (PA) are at increased risk of cardiovascular events. The objective of the present study was to evaluate the QT interval in patients with renovascular hypertension (RV) and PA before and after treatment. A total of 24 patients with RV and 38 with PA were studied; 89 patients with essential hypertension (EH) served as control group. Corrected QT intervals (QTcH) were measured from a 12-lead ECG. Basal QTcH was longer in RV (429±30 ms) and PA (423±23 ms) compared with EH controls (407±18 ms; P<0.001). The prevalence of QTcH >440 ms was higher in RV (29%) and PA patients (29%) compared with EH controls (4%; P<0.001). QTcH interval was evaluated after treatment in 19 RV and 15 PA patients. QTcH was reduced after renal-artery angioplasty in RV patients (419±14 ms; P=0.02), and after spironolactone or adrenalectomy in PA (403±12 ms; P=0.01). In conclusion, QT interval was prolonged in patients with RV and PA compared with controls with EH. After angioplasty of renal-artery stenosis in RV, and treatment with spironolactone or adrenalectomy in PA, the cardiovascular risk of such patients may be reduced by concomitant blood pressure lowering and QT duration shortening.