If i deal lethal damage to the enemy hero, and this triggers a secret that causes lethal damage to my hero, shouldn’t i win because i dealt lethal damage first?
No, it is a draw. 
1 Like
it gave me a loss, which ended my win streak
Well, you didn’t win, but you also didn’t lose. You don’t lose stars when you draw.
i dont recall if i lost a star or not. but it did say i was defeated. either way, my win streak ended, which is the only reason i care.
just for clarification…i attacked the enemy hero for 7 damage, which was lethal damage. this triggered my opponents “eye for an eye”, which dealt lethal damage to my hero.
i guess i just assumed that there was a “stack”, like in MTG
Quoting https://hearthstone.gamepedia.com/Gameplay#Conclusion
Both heroes’ health reaches zero at the same time. This causes a draw, although both players will see the Defeat screen. Neither player will win or lose a star in [Ranked] play, and neither player will be awarded a win or loss in [Arena] mode. If you were on a winning streak, it will end your streak.
If you used to MtG, you should understand game phases. Win condition is checked when whole “attack” phase is ended, i.e. after you both got lethal damage.
There is no special animation for a tie. So in the case of a tie, both players are shown the “defeat” screen.
But the game IS handled as a tie internally. Which means that you neither win nor lose a star in ranked, that your MMR is unaffected in ranked legendary and in casual, that you get neither a loss nor a win in Arena, and that in a solo adventure your run is not stopped but you don’t progress either.