There is a detailed post somewhere on the forums by a nice fella who tested all the defensive perks. Fortitude does work, and with half damage taken after your shield breaks, it becomes 450hp for three seconds. Which is roughly a quarter more hp during a 1v1.
On fire after winning a battle, giving you time to roll it off? Surviving lingering infector bugs by a hair? Thank you Fortitude!
For any type of consistent success in pvp you pretty much need to stack defensive perks; either to level the playing field against another defensive player, or to survive and beat the cloaked shotgunners.




