The aim of this study was to analyze the HR/QT relation during exercise in a group of patients with effort angina (Group B) in comparison with the same relation obtained in a group of normal subjects (Group A) comparable for age and sex. The regression analysis was carried out separately during effort in upright position and during rest in clinostatic position to avoid influences on QT by the patient's posture. During effort in patients of the Group B the regression shows a lower value of the slope and of the intercept (p less than 0.001) than those obtained in the subjects of the Group A. A similar behaviour is shown also from the regressions obtained during rest in the same groups. Thus at the highest HRs we observed a longer QT in the Group B. Moreover QT of ischemic patients in the presence of ECG signs of ischemia (ST less than or equal to 1 mm) resulted significantly longer (p less than 0.01) either during effort and at rest, respect to that obtained in Group A at comparable HRs. The analysis of the regression HR/QT after administration of atenolol 100 mg per os in a subgroup of patients of Group B clearly shows a less prolonged QT at the highest HRs where ECG ischemia frequently appears. This fact is demonstrated by the presence of a higher slope (p less than 0.05) respect to that obtained in the same group without therapy. In conclusion, myocardial transient ischemia provokes a longer QT in patients with ischemic heart disease in comparison with normal subjects. Acute therapy with atenolol per os is able to condition the regression HR/QT showing a relative shortening of QT at the highest HRs respect to that carried out in the same patients in absence of therapy.