You most likely hit the heart critically, but the game doesn't provide feedback if that happens 😅
Regarding QTEs, the cooldown only kicks in if you press a button at the wrong time. If you only press a button when it's red, there's no cooldown, and you can press as many buttons as you want. I was able to complete QTEs with >15 buttons one time.
Thank you for playing game! Hope you had fun!