New York Heart Association Class III or IV heart failure.

A history of heart failure induced by tachy-arrhythmia.

A history of coronary artery disease and the presence of at least one of the following:

* Canadian Class III or IV angina.

* Recent myocardial infarction, coronary artery bypass grafting, or percutaneous coronary intervention within 6 months.

Severe renal or hepatic impairment.

Subjects who have a clinically significant allergy/intolerance to atenolol, including a history of beta-blocker induced bronchospasm.

Females who are pregnant or nursing.

History of severe AV node dysfunction/pacemaker dependence.

Subjects who have a systolic blood pressure \< 90 mm Hg or resting Ventricular Rate \<50 or \>120 per minute on the day of the study.

Patients currently taking Vaughan-Williams Class I or III anti-arrhythmic drugs.

Genetically Determined Response to Atenolol in Patients With Persistent Atrial Fibrillation