This document discusses sodium channel blockers and their mechanisms and effects. Sodium channel blockers increase the threshold for excitation, decrease conduction velocity, and increase refractoriness. They can either suppress or exacerbate arrhythmias depending on their effects on conduction and refractoriness. Common sodium channel blocking drugs include lidocaine, phenytoin, and mexiletine. Adverse reactions include decreased conduction and worsening of arrhythmias in some cases. The document also briefly discusses other classes of antiarrhythmic drugs like potassium channel blockers, calcium channel blockers, adenosine, and vernakalant.