User blog comment:Slashingstrike/AP Item for Tanks/@comment-25281296-20161025143951

I'll say that the stats are worth itself over 3000 gold. And granting it two additional passives makes it even more powerful - with the stats granted by this item itself, the bonus to Ability Power equals to 24 and allows you to deal bonus 120 damage over three seconds on most of your spelld, also healing you by another tremendous amount.

It might be bad idea, but compare it to Smite's Ethereal Staff, where it grants 400 health, 300 mana, 30 magic power and 1,5% of health as additional magic power. The stats in mentioned item are worth a bit over 2200, and the pasive makes it good enough for tanks.

Back to your item, as you can see you should tone down the stats it grants, while also removing one of the effects (as both are really strong). I would suggest decreasing bonus AP to 40 and remove the second effect.

Now, to compare: Imagine exemplary Maokai: Full tank build (no AP from items other than Undying Heart) with Undying Heart, results in ~200 armor and mresi, 4000 health. He will then have: 136 AP (with my suggestion 116) and spellcasts once every 5 seconds will deal bonus 380 damage over three seconds, possibly healing by up to 600 health. Not only too much damage, but also too much healing and durability, making this item mandatury on all ap tanks and bringing back tank's meta.

What'cha thinking? :P