Your heart muscles will not get eaten up until after you have fasted to completion. That is why you need to take it a day at a time. The people you are talking about sound very ignorant. Your body will tell you when you have fasted to completion and then you will need to start refeeding. Yes, your body is having a feast off of itself, but I guarantee you it is not your heart at this point. Your body is eating fat, viruses, bacteria, parasites, scar tissue, tumors, unwanted growths, and any disease material it can find. When there is nothing left for it to eat except what you need, like your heart, true hunger returns and you will have fasted to completion. You will need to start eating again at this point. I had the same problem with people when I was your age. They really messed me up and I stopped fasting for years. I know now how foolish they were and how foolish I was to let them control me and for me to believe them. I so regret it. It really messed me up. You are doing the right thing, just forget about the 40 days and take it a day at a time.
Rainy