Widget doesn't refresh on input

I’m creating a very simple health bar with hearts, making the number of hearts visible as the value of player’s health (in my case 3 hearts)


The initial bar is generated correctly, but after that when I lower player’s health, the visibility of the single hearts doesn’t change.
I’m new to UE4 and I’m wondering if I’m missing anything important here

This is what I have in my character blueprint on BeginPlay

Then, in my widget diagram, I have the following

And in my character blueprint, I call the UpdateHealth like this

The Event Construct in my widget is called as I’m expecting, creating the amount of visible heart as the current health of the player, but when I press D to apply damage, UpdateHealth is called (I initially created a print string to be sure), but the visibility of the widget doesn’t change at all.

Found my own solution