The local anesthetic-class of anti-arrhythmic drugs block the inward sodium current in nerve and cardiac muscle. A number of models for the interaction of these drugs with the neuronal sodium channel have been extended to cardiac muscle. The models assume a single binding site for the entire class of agents. The kinetics of drug interaction with this site depend on the Na channel conformation, open and inactivated channels having greater affinity than resting channels. An alternative formulation considers drug-receptor affinity as fixed, but access to the binding site is controlled by channel gating. Several clinically relevant predictions, such as competitive displacement of multiple agents, can be made from these models.