Atrial fibrillation is a condition where the atrium (top chambers of the heart) are no longer allowing organized electrical activity.  

Rather, there is a random oscillation of electrical waves that do not allow the atrium to contract as they should.

 The Atrioventricular Node (AV Node) responds to this haphazard electrical activity in a very irregular and rapid pattern, causing a very irregular, rapid heart (pulse or ventricular response) rate.  

This condition is typically the result of severely dilated chambers.  

This condition can rarely be corrected; however, the ventricular response rate can be lowered to a reasonable level with medications, frequently the combination of Digoxin and Diltiazem.

Continued rechecks and monitoring for adequate heart rate control are essential to ensure these patients remain at an optimal heart rate and do not develop congestive heart failure (fluid in the lungs).