Myocardium innervation

This group consists of j3-adrenergic receptor blockers, the antiarrhythmic activity of which is associated with inhibition of adrenergic innervation action of the circulatory adrenaline on the heart. Because all 8-adrenoblockers reduce stimulatory sympathetic nerve impulses of catecholamines on the heart, reduce transmembrane sodium ion transport, and reduce the speed of conduction of excitation, sinoatrial node and contractibility of the myocardium is reduced, and automatism of sinus nodes is suppressed and atrial and ventricular tachyarrhythmia is inhibited. 

The heart is innervated by both sympathetic and parasympathetic nerve fibers of the autonomic nervous system. Although the heart can generate its own heartbeat independently of nervous control, stress, exercise, and physical trauma make it advantageous to adjust cardiac contraction to meet the needs at the time. Thus, the cardiovascular control system (Figure 6.20.5), which is located in the brain, controls the contractility of the myocardium (the muscle of the heart), and produces both inotrophic (force of contraction) and chronotrophic (rate of contraction) effects. 

---