Procedure performed when patient is in "uncontrolled" atrial fibrillation. (the cardiac rhythm is erratic – no longer regular). Patient is sedated to "dozing". In a controlled setting, the heart is given an electrical shock to convert back into a normal rhythm. The sedation may then be reversed, or allowed to wear off. The procedure may be performed on an out-patient basis - the patient is observed for a few hours (approximately 2-6), until determined it is safe to leave the hospital. Procedure length of time is approximately 20-30 minutes.