Electrical measurements of current flow in ventricular myocardium immersed in silicone oil showed that angiotensin II increases the cell-to-cell spread of current within seconds. The increases in current spread and conduction velocity occur without any changes in resting membrane potential or maximum rate of rise of the action potential. The concentration range was 10 nM to 10 μIM, with an ED50of 100 DM for angiotensin exposures lasting about 10 seconds. The largest effects were an apparent decrease in resistance through the cellular pathway to 50% of control and a 40% increase in conduction velocity, which returned to control in about 15 minutes. Continuous or repeated exposure to angiotensin caused desensitization to appear. These effects were found with or without denervation by 6-hydrox-ydopamine and β-adrenergic blockade by 1 μM propranolol in calf, pig, sheep, and rabbit ventricular myocardium. Therefore, angiotensin appears to increase electrical conduction rapidly and directly in cardiac muscle by decreasing resistance through the cellular pathway.Circ Res 47: 524-529, 1980