How do you stop arrhythmia with medication?

Carefully. There are 2 major classes of medications for fast arrhythmias: those that slow the heart rate and those that change ion fluxes of heart muscle. The first class is inexpensive and very safe. The second class is expensive and can have serious side effects but may be more effective & necessary in some cases. Slow arrhythmias cannot be treated with medication and may require a pacemaker.