Driver's Side Mirror Heater
 

So, I'm in Chicago and had to suffer the -50 degree (wind chill) week last week.

While driving around, I noticed that my driver's side mirror only had a small quarter size heat circle working. Obviously the rest of the heater isn't working. I didn't know the heater was a bunch of small circles (I'm assuming based on the one that is working).

The passenger mirror was working fine.

Any suggestions on how to go about troubleshooting that? Or would I have to replace the whole mirror?

What is the year of your car? It's need to get the right answers