Did you get over highest score in the game? And, are you sure you hadn't already gotten the heart?
Otherwise: No idea from me.
It's heart 62 right? I beat the high score by over 300 points and I never got the heart (I'm playing on Masterful)
I know I'm a couple of years late, but I finally beat the JumpBox game and got the high score. I did not receive a heart and am still missing number 62. It is the only heart I'm missing. Maybe there's a glitch in the game where this can't be the last heart you earn???? Very frustrating to be stuck at 99%!!