Well how long it takes really depends on how long it takes the oil that makes it spread to dry up. but rub it down with alcohol a few times a day or gas. if that doesnt work go back to the doctor and ask for a shot to get rid of it. after that it will take a couple hours to start working. you could also have it in your blood stream and therfore really the only way to get rid of it is to get a shot

First of all, do not use heat! That spreads it!
I used to get poison ivy REALLY bad as a child. My mom used a cotton ball and rubbed Clorox bleach on the rash and it cleared up within days! Do this 2 times per day until it is all gone!

Heat is a bad idea! I get poison ivy very bad and the best thing Iv'e found is tecnu. You can get it at any pharmacy for $15 and it is worth it! Make sure you follow the directions though and rinse only with cold water. Also rubbing alcohol helps.