This is a prospective cross-over trial that will enroll eligible patients with CPVT and perform a baseline treadmill exercise tolerance test (ETT) followed by a repeat treadmill ETT with I.V. atropine administered immediately prior to exercise. Atropine is a parasympathetic blocker and results in sinus tachycardia, which is expected to reduce the diastolic interval thereby reducing delayed after depolarizations and ventricular ectopy compared to baseline. Both ETTs will be performed on the same day with two hours of rest scheduled between ETTs. The primary analysis will be a paired comparison of the number of ventricular ectopic beats recorded during exercise (and recovery) at baseline and following pre-treatment with atropine. Secondary endpoints will include the presence of ventricular ectopy (yes/no), complex ventricular ectopy (couplets or greater, yes/no), and the number of runs of complex ventricular ectopy.