First of all, thanks to dr. lex for making this interesting model.
I referred to his guide on flexi and made this flexi heart

In the 3mf file I provided, the two models just "touched" together instead of being combined( there may be a warning when slicing that the object is too close, you can ignore it.), so the colors can be set separately and then printed together.

You can select both models at the same time and then zoom in or out together. It is not recommended to move one of the models separately, otherwise the printing result may not be as expected.

I only tested PLA+, other materials may need to be tested by yourself.

The last thing i want to say is “Wellcome to Rex world.”
In these few days, I saw many rex born in MW, so I also added one. Maybe one day, this will really become the world of rex, so I said that.
And I saw that some people have a wrong understanding of the shared license of this model.
like this：

But I think these people may have made an honest mistake, and it would be great if they could correct it.