Mega Man X4/Gameplay

Health
You'll only start out with 16 hit points, but you can increase your maximum by acquiring Heart Tanks. Sub Tanks are also available to help keep you alive.

Heart Tanks
Heart Tanks are permanent power-ups that increase your maximum health.

Sub Tanks
Sub Tanks are permanent power-ups that allow you to fill up a reserve amount of health. You can use the contents of a Sub Tank at any time; however when used you must use it until either it is empty or your health is full.