1. Hypertension leads to electrophysiological changes in the heart. Chronic exercise induced by a treadmill‐running program (TRP) is considered as a potential non‐pharmacological treatment for hypertension and may have implications in heart remodeling. However, it is not known if TRP is able to improve the electrophysiological properties of the heart in spontaneously hypertensive rats (SHR). In the present study, we tested whether TRP affects the electrical properties of left ventricular (LV) myocytes isolated from different layers of the LV wall of SHR.2. Male SHR were divided into exercised (chronic treadmill running for 8 weeks; CEX‐SHR) and sedentary (SED‐SHR) groups. Age matched normotensive Wistar male rats served as controls. Action potentials (AP) and transient outward potassium current (Ito) were recorded in sub‐epicardial (EPI) and sub‐endocardial (ENDO) LV myocytes.3. We found that in normotensive controls, AP duration (APD) in ENDO cells were longer than in EPI cells. Such a transmural heterogeneity in LV was not observed in sedentary SHR but was partially restored in SHR subject to chronic exercise. This partial recovery was associated with an increase in Ito density in EPI cells but not in ENDO cells. The electrophysiological changes observed in the CEX‐SHR group were not accompanied by amelioration of systolic blood pressure neither by reduction in heart hypertrophy.4. These findings imply that TRP is able to improve electrophysiological parameters of isolated cardiac myocytes in SHR. Such adaptation contributes to an overall improvement of heart physiology in this model.© 2012 The Authors Clinical and Experimental Pharmacology and Physiology© 2012 Blackwell Publishing Asia Pty Ltd