The cellular mechanism of premature ventricular contractions (PVCs) is unknown. The investigators have previously observed that 5% of patients in the investigators electrophysiology laboratory with ventricular outflow tract PVCs have inducible sustained ventricular tachycardia that behaves in a manner similar to patients who present clinically with sustained ventricular tachycardia, i.e., sensitive to adenosine and triggered activity. This suggests that outflow arrhythmias may be a continuum of a single mechanism. To further determine the mechanism of frequent PVCs, the investigators will determine the effects of pharmacologic agents administered prior to catheter ablation.