The purpose of this study is to learn the effects of a test drug on heart rhythms, which may become life-threatening if left untreated, and to provide data to see if the drug is well tolerated and safe.

Inclusion Criteria:

• Patients with or without ICDs (implantable cardioverter defibrillators)
• Patients undergoing an electrophysiology study for evaluation of ventricular rhythm
• Patients with a history of heart disease

Exclusion Criteria:

• Patients with uncontrolled blood pressure
• Patients with certain cardiac risk factors
• Patients with significant kidney or liver problems