The class II drugs include the entire family of beta-adrenergic blocking agents. These drugs bind to beta-adrenergic receptors rather than binding directly to specific ionic channels. For this reason they affect those regions of the heart that are most sensitive to variations in beta-adrenergic tone. These include the sino-atrial and the atrio-ventricular nodes, the regions regulated by the balance of beta-adrenergic (B) and parasympathetic (P) effects. In this way, the beta adrenergic blocking agents affect sinus rate and AV nodal conduction and refractoriness.
