For the first card, you don't care whether you get an Ace, King, Queen, Jack or 10 of hearts. So you can get any of those cards. So you can get any of these 5 cards
Then on the second card, you can only accept 4 cards. Lets say you got a 10. Well then for the second card you need an Ace, King, Queen, or Jack of hearts. So thats 4 possible. Since you already have 1 card though, there are only 51 cards remaining. This pattern repeats
Then for the third card, you can only accept 3 out of the possible 50. For the 4th 3 possible and for the 5th card, 1 possible.