This was quite easy and perfect for when you want a quick sewing project.
So I first I laid out a piece of fabric (on the fold as shown below).
I drew out the first one and liked the size and traced two more out of that one.
I added an additional 1/4" around the hearts for seam allowance to turn them inside out.
For size reference:
I sewed all around the heart & clipped the extra fabric away.
Then turned it inside out.
I pinned the first heart to the middle of the shirt. Then the other two hearts, I placed two fingers away from the middle one.
Then just a simple zig zag stitch around each heart & done!