Question about UMG

Hello,guys! I encounter some problems about the UMG image won´t display the right result.
The first texture is the UMG I create,the brush image I use a material.

The second texture us the blueprint of this UMG. I want use the variable ‘healthv’ to control the Image,but did not work.497e4532f11e8093949217e81b18e3deeb0ca953.png
How to solve this problem?thanks!!