This resource allows you to view the health of another player / living entity in your action bar as heart symbols, not just numbers, when you damage them. It also allows you to continue viewing their health a few seconds after you last hit them.
To reduce lag it limits the max displayed hearts to 30.
Has a rate limiter to reduce the while loops happening per player.
Everything is customizable including colours for hearts / half hearts / empty hearts / dead hearts, heart symbol (must be pasted in UTF-8 format), display name and players only.
There is an option to view health in chat instead of action bar
If you wish, you can use SkRayfall to have a below name health hologram for all players, this also has options. - Just remove the # from the start of these lines at the bottom of the resource

Works on all versions with Skript 2.5.3 on 1.9.10+
or Skript 2.5.3 1.8 for 1.8.8