In PVP you won’t often get the chance to aim his skill on a full-health target. He doesn’t reduce 85K if the enemy isn’t at full health. If the enemy already lost 100K he won’t reduce any health at all.
A hero has 300k base health. He starts the match with 400k because of Heimlock’s gold passive.
By the time Heimlock’s gold ends, he is at 300/400k (75%HP), so he won’t stay at 300/300k but 225/300k (75%). He gets further damaged down to 150k HP (50%) Heimlock’s uses sterilize and increases his health by 30k. Now his max health is 330k, but he will still be at 50%, so his current health is increased to 165/330k
The way these skill works make them great for healthy heroes and useless for hurt heroes