Inclusion Criteria:

AF patients undergoing catheter ablation - Group A

1. Patients with AF scheduled to undergo a catheter ablation at the Mayo Clinic, Rochester will be approached.
   1. Patients undergoing percutaneous catheter ablation for AF at the Mayo Clinic, Rochester.
   2. Aged between 50 and 90 years

Non-ablated AF controls – Group B

1. Controls in group B will be matched to AF ablation subjects (group A) for age, gender and duration of AF.
2. Controls will be derived from those already enrolled in the Mayo Clinic Study of Aging.
   1. If an appropriate matched control is not identified in the Mayo Study of Aging, subjects will be recruited from those visiting Cardiology outpatient clinic at Mayo Clinic, Rochester with diagnosis of AF based on electrocardiographic documentation of rhythm reviewed by a board certified Cardiologist.

Group C

1. Patients of age > 18 years referred for ablation in the left heart for ventricular arrhythmia including ventricular tachycardia, premature ventricular contraction and ventricular fibrillation.

Exclusion Criteria:

AF patients undergoing catheter ablation - Group A

1. Prior history of dementia
2. Diagnosis of dementia based on baseline testing at enrollment
3. Presence of implantable cardiac electronic device such as implantable cardioverter defibrillator (ICD) or pacemaker in a pacemaker dependent patient and other non-MRI compatible implanted devices that will preclude MRI.
4. Pregnant women
5. Prisoners
6. Unable or unwilling to provide informed consent.

Group C

1. Patients who are unable to undergo MRI imaging due to the presence of any one of the following devices:
   • Implantable cardioverter defibrillator or pacemaker if the patients is pacemaker dependent and the device is not MRI compatible
   • Other implantable devices such as deep brain stimulator, aneurysm clip, intra-thecal pump, vagal nerve stimulator and programmable ventricular shunt.
2. Presence of intracardiac thrombus on transthoracic or transesophageal echocardiogram prior to the ablation.
3. Pregnant women
4. Prisoners
5. Unable or unwilling to provide informed consent.