All you need to do is make a mask.
This might help:
Step 1 - Size both files to the same approximate size and resolution.
Step 2 - Set the color mode to the same for both files.
Step 3 - On the heart file, select the interior part of the photo > Save selection.
Step 4 - Select the entire portion of the picture file you want to position inside the heart shape > Copy.
Step 5 - Return to the heart file and load the saved selection > Edit > Paste into.