I am new to MTG and this has been bothering me. Say I use any spell on my 1st main phase to deal 1 damage to my opponenent's 2/5 creature.
If I attack him during the combat phase of the same turn with a 4/3 creature and he blocks me using that 2/5 I previously did 1 damage to, will my 4/3 creature kill it, or his creature would have "healed" up between phases?