Leonardo Da Vinci Help?

I Have been asked to write a letter from da vinci to the royal society of science about his discoveries on blood circulation and the heart, however, I JUST CAN'T FIND ANY SITES WITH ENOUGH INFO!!! Sure, they'll tell me that he DID do the experiments. But WHAT did he do? HOW did he prove it! I need to know some good sites! Or at least give me some info!