Lifesteal

Lifesteal is a form of self-healing derived from damaging the enemy. When you don't have enough healing from external means you simply assault the enemy to restore health to yourself. Some Heroes, like The Butcher, are completely reliant on their self-healing to survive.

The healing is calculated based on the damage the target takes, meaning that as the damage is affected by damage modifiers on the attacker (e.g. Spell Power) or target (e.g. Armor), the healing amount is affected as well. There are multiple types of lifesteal, but the two general types are Basic Attack lifesteal and Spell lifesteal. Damage dealt by a spell will heal no health from attack lifesteal, and the same with the other way around.

All healing received from lifesteal is affected by healing modifiers. While damage taken from Percent damage as the source of lifesteal healing can not affected by damage modifiers, the healing received from it is still affected by healing modifiers. Effects that heal a flat amount of Health or a percentage of your or the healer's Health are not lifesteal effects.

Attack Lifesteal

 * Alarak's level 1 talent "Overwhelming Power" grants 50% lifesteal for 4 seconds after hitting a hero with "Discord Strike".
 * Anub'arak's level 7 talent "Leeching Scarabs" grants Scarabs 50% lifesteal that heals Anub'arak.
 * The Butcher's "Butcher's Brand" grants 75% lifesteal against the target doubled against heroes for 4 seconds, increased by .5 with each attack against heroes.
 * Cassia's level 4 talent "Ring of the Leech" grants 15% lifesteal.
 * Deathwing's level 1 talent "Draconic Might" grants 25% lifesteal.
 * D.Va's level 1 talent "Full Metal" grants 20% lifesteal against enemies within the bonus damage area of "Fusion Cannons".
 * E.T.C.'s level 1 talent "Guitar Hero" grants 50% lifesteal for the duration of Guitar Solo.
 * Falstad's level 4 talent "Hammer Gains" grants 20% lifesteal from the primary target.
 * Illidan's trait "Betrayer's Thirst" grants 30% lifesteal.
 * His level 4 talent "Thirsting Blade" increases healing to 50% of damage dealt while "Sweeping Strikes" bonus is active.
 * Lúcio's level 1 talent "Smooth Moves" grants 30% lifesteal while "Wall Ride" is active.
 * Mal'Ganis's level 1 talent "Vampiric Aura" passively grants nearby allied heroes 15% lifesteal from all physical damage dealt.
 * Medivh's level 7 talent "Mystic Assault" makes his "Arcane Rift" grant 40% lifesteal to the next basic attack within 6 seconds if a hero is hit.
 * Orphea's trait "Overflowing Chaos" makes hitting a hero with basic ability grant her next basic attack 100% lifesteal against a hero.
 * Qhira's level 7 talent "Siphoning Link" grants 20% lifesteal.
 * Rehgar's level 10 heroic "Bloodlust" grants nearby allied heroes 30% lifesteal from the primary target for 6 seconds.
 * Rexxar's level 20 talent "Spirit Bond" grants Misha 50% lifesteal that heals Rexxar for 18 seconds.
 * Sgt. Hammer's level 4 talent "Regenerative Bio-Steel" grants 10% lifesteal in Siege Mode.
 * Sonya's level 1 talent "War Paint" grants 30% lifesteal.
 * Tracer's trait "Reload" grants 10% lifesteal.
 * Her level 4 talent "Leeching Rounds" increases the lifesteal based on her missing health, up to 200%.
 * Tyrael's level 4 talent "Divine Vigor" grants 50% lifesteal for 4 seconds if Smite hits an enemy.
 * Tyrande's level 7 talent "Elune's Chosen" grants 200% lifesteal that heals the target ally for 10 seconds.
 * Valla's level 13 talent "Tempered by Discipline" grants 25% lifesteal at full Hatred.
 * Varian's level 7 talent "Second Wind" grants 50% lifesteal while below 50% health.
 * Xul's level 7 talent grants him 70% lifesteal from heroes while "Cursed Strikes" are active.
 * Zeratul's level 13 talent "Mending Strikes" grants 35% lifesteal.

Spell Lifesteal

 * Ana's Trait "Shrike" has 50% lifesteal.
 * Ana's level 20 talent "Nano Infusion" makes her heroic "Nano Boost" grant target allied hero 50% lifesteal for 8 seconds.
 * Anduin's level 20 talent "Varian's Legacy" adds a Damage over Time effect to his Basic Attack that has 50% lifesteal.
 * Blaze's level 16 talent "Heat Treatment" grants his trait "Pyromania" 75% lifesteal.
 * Cassia's level 4 talent "Ring of the Leech" grants 15% lifesteal on Lightning Fury and Fend if the target is Blinded.
 * Deathwing's level 1 talent "Dragon Soul" grants "Incinerate" 75% lifesteal and the explosion of "Lava Burst" 150% lifesteal against heroes.
 * Diablo's "Fire Stomp" has 125% lifesteal against heroes.
 * His level 4 talent, "Souls to the Flame", increases this lifesteal by 1.25% per Soul.
 * Diablo's level 20 talent "Lord of Terror" steals 10% of the maximum Health of nearby enemy Heroes.
 * D.Va's level 4 talent "Rush-down" causes "Boosters" to steal 2% of the maximum health of Heroes it hits.
 * Gazlowe's "Deth Lazor" heals him for 25% of the damage dealt, increased to 75% against Heroes.
 * Gazlowe's 4 talent "Hyperfocus Coils" causes "Deth Lazor" and "Xplodium Charge" to deal bonus damage against Heroes based on their maximum Health and heal Gazlowe for 150% of the bonus damage dealt.
 * Illidan's level 7 talent "Hunter's Onslaught" grants his basic abilities 25% lifesteal, doubled against heroes.
 * Imperius' Basic Ability "Molten Armor" heals for 100% of the damage dealt, doubled against Heroes.
 * His level 13 talent "Heat of Battle" causes it heal 25% more while low on Health.
 * Kel'Thuzad's level 4 talent "Phylactery of Kel'thuzad" grants 10% lifesteal when charged.
 * Leoric's level 20 talent "Spectral Leech" causes basic attacks to deal bonus spell damage equal to 2.5% of the target's max health and heal for twice that amount.
 * Mal'Ganis's level 7 talent "Will of Tichondrius" causes third slash of "Fel Claws" to deal bonus damage equal to up to 4% of the affected Heroes' max health and heals for 100% of the damage dealt, based on the enemies hit by the first two slashes.
 * Malthael's level 20 talent "Angel of Death" causes his heroic "Last Rites" to restore health equal to the damage dealt.
 * Mephisto's level 7 talent "Hateful Mending" grants his "Skull Missile" 50% lifesteal against heroes.
 * Orphea's level 16 talent "Bond of Anguish" causes her "Shadow Waltz" ability to deal bonus damage to enemy heroes equal to 3% of their maximum health, healing for 50% of the damage dealt.
 * Qhira's level 7 talent "The Thirst" grants her "Carnage" ability 50% lifesteal against heroes.
 * Ragnaros' "Empower Sulfuras" has 20% lifesteal doubled against heroes.
 * His level 13 talent "Cauterize Wounds" grants additional 40% lifesteal against heroes over 2 seconds.
 * Raynor's level 16 talent "Paint Them Red" grants "Penetrating Round" 90% lifesteal against heroes.
 * Sonya's "Whirlwind" has 25% lifesteal tripled against heroes.
 * Her level 13 talent "Life Funnel" increases Whirlwind base lifesteal to 35%.
 * Thrall's level 7 talent "Ancestral Wrath" deals 15% of the target's max health in damage over 3 seconds and heals for 150% of the damage dealt.
 * Tychus' level 13 talent "That's the Stuff!" grants his trait "Minigun" 100% lifesteal once it expires.
 * Valla's level 13 talent "Siphoning Arrow" grants "Hungering Arrow" 75% lifesteal against heroes.
 * Xul's level 20 talent "Andariel's Visage" grants his heroic "Poison Nova" 50% lifesteal.
 * Zeratul's level 20 talent "Shadow Mending" grants 75% lifesteal against heroes.

Other forms of Lifesteal

 * Hogger's level 13 talent, "Bloodthirst", heals him for 33% of the damage dealt to Heroes by basic attacks, "Staggering Blow", and "Hogg Wild".
 * Mal'Ganis' trait "Vampiric Touch" heals him for 15% of all damage dealt except for "Will of Tichondrius" and "Dark Conversion", increased to 45% against Heroes.
 * His heroic ability, "Carrion Swarm", increases the lifesteal against Heroes to 75% for its duration.
 * His level 4 talent, "Fueled by Torment", makes "Necrotic Embrace" increase the lifesteal against Heroes by additional 15% for its duration.
 * His level 20 talent, "Vanquish the Weak", increases the lifesteal by additional 10% against slowed Heroes.
 * Malthael's "Soul Rip" restores health equal to 4% of the target's max health (does not drain this health).
 * His level 13 talent "Soul Siphon" increases Soul Rip healing to 4.75% of the target's max health.
 * Murky's level 13 talent, "Fish Tank", grants him 25% lifesteal for both basic attacks and basic abilities.
 * Whitemane's trait "Zeal" heals affected allied Heroes for 100% of all damage she deals to Heroes.
 * Her level 1 talent, "Pity the Frail", increases this lifesteal to 125% for allied heroes below 50% health.
 * Zul'jin's level 20 talent "Amani Resilience" grants him 50% lifesteal for all damage dealt while his heroic "Taz'dingo" is active once it expires.

Related mechanics
Some abilities act similarly to Lifesteal but convert the damage into other type of resource than Health:
 * Auriel's trait, "Bestow Hope", converts 8% of all damage dealt by her and target allied Hero into Energy, increased to 40% against Heroes.
 * Her level 7 talent, "Energized Cord", increases the energy gained from Auriel's basic attacks to 40% of the damage dealt, increased to 100% against Heroes.
 * Fenix's level 13 talent, "Auxiliary Shields", converts 10% of the basic attack dealt into Shields.
 * Jaina's level 13 talent, "Ice Barrier", converts 25% of the spell damage dealt to Chilled targets into Shields.
 * Kerrigan's trait, "Assimilation", converts 10% of all damage dealt into Shields, doubled against heroes.
 * Her level 1 talent, "Fury of the Swarm", increases this amount by 10% when applied to basic attacks.
 * Her level 13 talent, "Volatile Power", increases this amount by 10% but reduces the duration of the Shields.
 * Her level 20 talent, "Psionic Shift", allows her to teleport and damage nearby enemies, converting 300% of the damage dealt into Shields.
 * Mephisto's level 4 talent, "Static Barrier", converts 40% of the damage dealt by "Lightning Nova" to Heroes into Shields.
 * Ragnaros' level 13 talent, "Tempered Flame", converts 100% of the damage dealt by "Blast Wave" ability to Heroes into Shields.