Here is an except from this website: http://www.bostonscientific.com/templatedata/imports/HTML/CRM/patient/
"How can a magnet affect my device?
A magnet can also cause your implanted device to respond differently if your device gets within six inches of the magnet. Your defibrillator will respond to a magnet based on how your doctor has programmed your device to respond. A pacemaker will respond by temporarily pacing at a different pre-set rate. Ask your doctor for more information.
Note: If you have a defibrillator, some strong magnetic fields may cause your device to make beeping tones. If you hear beeping tones from your device, you should:
Immediately move away from the object that may be causing the beeping.
Call your doctor to report the beeping."