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Cannabidiol (CBD) is a non-psychoactive component of Cannabis which has recently received regulatory consideration for the treatment of intractable forms of epilepsy such as the Dravet and the Lennox-Gastaut syndromes. The mechanisms of the antiepileptic effects of CBD are unclear, but several pre-clinical studies suggest the involvement of ion channels. Therefore, we have evaluated the effects of CBD on seven major cardiac currents shaping the human ventricular action potential and on Purkinje fibers isolated from rabbit hearts to assess the in vitro cardiac safety profile of CBD. We found that CBD inhibits with comparable micromolar potencies the peak and late components of the Na V 1.5 sodium current, the Ca V 1.2 mediated L-type calcium current, as well as all the repolarizing potassium currents examined except K ir 2.1. The most sensitive channels were K V 7.1 and the least sensitive were K V 11.1 (hERG), which underly the slow (I Ks ) and rapid (I Kr ) components, respectively, of the cardiac delayed-rectifier current. In the Purkinje fibers, CBD decreased the action potential (AP) duration more potently at half-maximal than at near complete repolarization, and slightly decreased the AP amplitude and its maximal upstroke velocity. CBD had no significant effects on the membrane resting potential except at the highest concentration tested under fast pacing rate. These data show that CBD impacts cardiac electrophysiology and suggest that caution should be exercised when prescribing CBD to carriers of cardiac channelopathies or in conjunction with other drugs known to affect heart rhythm or contractility., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)