From the testimony given, the analyst found heart shaped residue while using an instrument on the duct tape. She had a supervisor concur with her about what it looked like, but because of the other tests being done on the tape, the residue apparently was lost, so they could not get the image to show up again. No pictures were taken, and it doesn't appear that the heart shaped sticker that matched this particular image was ever found (at least they never presented it into evidence).
So, I guess, no they didn't hammer it home, although having the expert testify to it, and having a supervisor confirm what they saw, I, suppose, is good enough. As someone said yesterday, the tests being done on the duct tape that destroyed the heart image, were far more important than the heart image itself.