The acute effects on monophasic action potentials (MAP), QT interval, and right ventricle effective refractory period (V-ERP) of propranolol 0.2 mg.kg-1 body weight have been studied in 10 patients with coronary artery disease. The median duration of MAP at 90% repolarization (MAP90) was shortened from 238 to 228 ms at a constant paced heart rate of 100 beats.min-1, while V-ERP remained unchanged. The median ratio V-ERP/MAP90 increased from 1.00 to 1.03. The electrical restitution curves of the duration of premature action potentials, normalized to those paced at constant heart rate, were more horizontal after propranolol. Isometric handgrip shortened MAP90 from 217 to 211 ms and after propranolol similar shortening was found (215 to 209 ms), although both values were slightly lower than before beta-blockade.