It is best to avoid entering combat with low health, unless Bloodwell is so full that enough health can be recovered to continue fighting.
Lifesteal can be very powerful on Aatrox to offset his living costs.
Massacre is ideal for turning the tables in combat; it's important to use it at the right time to get the most out of it.
Playing against Aatrox
When Aatrox suffers mortal damage, he heals the amount currently present in his resource bar; if he is given the knockout blow when the resource bar is almost empty, he will revive with a much lower amount of health.
When Aatrox lanaz Darkflight towards your position, avoid being knocked down by moving away from the center of impact.
Aatrox relies heavily on his basic attacks to deal damage and survive; Reducing your attack speed by purchasing Omen of Randum or Heart of Ice allows you to noticeably reduce both components.