Just started watching the Hulk hero pack stream and saw the +4 hit points card. It caused me to question how it works? Would that increase his max health to 22 or does it function like the recovery basic power?

I have been playing the Iron Man cards as an increase to max hit points, meaning later in the game he can use recover to heal back up to 15, so I'm wondering if I have been playing wrong. As always, thanks for any replies.

You have been playing it correctly. When you play the card you add 4 to your current hit points and as long as the card is in play you have +4 to your maximum hit points. If the card leaves play for any reason, you immediately decrease your current hit points by 4.