Class IB antiarrhythmic drugs include drugs such as lidocaine, mexiletine, and phenytoin sodium, which mainly shorten the action potential. Anti-arrhythmic drugs mainly terminate episodes of arrhythmia or improve patient prognosis by reducing arrhythmias. Lidocaine is mainly hemodynamically stable for ventricular tachycardia, ventricular fibrillation, but often causes vertigo, impaired consciousness, and excessive suppression of the sinus node of the heart, and is no longer the drug of choice. Mecillin is useful for the treatment of acute and chronic ventricular tachycardia with a combined QT interval, but can often cause nausea, vomiting, hypotension, bradycardia, and other problems that require cardiac monitoring. In case of hemodynamic instability, treatment by electrical resuscitation can only be considered.