Which anti-arrhythmic medication is best to control frequent, non-sustained, monomorphic ventricular arrhythmias with a structurally normal heart ?

May need nothing: Unless causing symptoms or a cardiologist finds some.underlying abnormality what you describe does not need treatment. Caffeine, lack of sleep, stress, alcohol and decongestants like pseudofed, and energy drinks will all exacerbate the problem. If it needs treatment a beta blocker like Metoprolol or Coreg (carvedilol) are good choices Too much thyroid medication can bring this out as well.