I went to my cardiologist on day one. Okay, he thought I was loopy but said my heart would be happier for it (with the weight loss). I'm doing a blood check next week to see how it effects my cholesterol levels, etc. I'm kinda excited about that one.
In any case, if you have a condition, it's always good to get your doctor involved. Even if you just call the office and talk to the nurse. Don't go about it like you're not going to eat for 10 days, but present it as a cleansing period and see what he/she says.