One way: You can make another copy of your PNG that is solid (no transparency inside), parent it to the one you want to show, and use it as a track matte.
See here (down the page a ways) for more on how track mattes work. After Effects Help | Alpha channels, masks, and mattes
Look at Auto Trace. Very handy.
If your heart shape as an outline you will need a copy of it that has the center filled. Use that copy as a track matte. If you make your open heart shape shrink using scale you can simply make the open heart the parent of the solid heart. The solid heart could be used as a track matte for an adjustment layer. You could also use the track Matt to knock a hole in a blurred copy of your main footage.
This is nothing more than masking and layers.
Rick, your last tip gave me what I needed, thank you.
I suppose that's also