Selective blocker of NaV1.5 channels (IC50 = 348 nM); displays no effect on other isoforms, including NaV1.2, NaV1.4, NaV1.6 and NaV1.7. Thought to inhibit sodium channel activation by binding to the NaV1.5 S3-S4 linker of domain II. Selectively inhibits the activation of cardiac sodium channels, but has no effect on sodium channels in dorsal root ganglion neurons.