objective: Eugenol is a natural compound found in the essential oils of many aromatic plants. The compound is used as a local anesthetic because of its inhibitory effect on the voltage-gated Na channels (Na), which are expressed in the nociceptive neurons. Eugenol has shown wide range of activities in the cardiovascular system; most of these activities are attributed to the modulation of voltage-sensitive Ca channels. However, its action on Na1.5, the main subtype of Na expressed in the mammalian myocardium, is unknown. The interaction of eugenol with Na1.5 could also contribute to its antiarrhythmic properties in vitro and ex vivo. We investigated the compound's effect on sodium current (I) and its possible cardiac antiarrhythmic activity. methods: The effect of eugenol on cardiac contractility was investigated using isolated atrium from guinea pig (for isometric force measurements). The compound's effect on I was evaluated using human embryonic cell transiently expressing human Nav1.5 and patch-clamp technique. results: Eugenol caused negative inotropic and chronotropic effects in the atria. In the ex vivo arrhythmia model, eugenol decreased atrial pacing disturbance induced by ouabain. Eugenol reduced the I in a concentration-dependent manner. Furthermore, the compound left-shifted the stationary inactivation curve, delayed recovery from inactivation of the I, and preferentially blocked the channel in the inactivated state. Importantly, eugenol was able to attenuate the late sodium current. All these aspects are considered to be antiarrhythmic. conclusions: Overall, our findings demonstrate that eugenol has antiarrhythmic activity due, at least in part, to its interaction with Na1.5.