It's a bit tricky without seeing the icon or your layers to say what the problem is. Flashing would suggest that perhaps you're using layers with some transparency and have your disposal set wrong. If all of your layers are complete and show the entire icon then make sure the disposal is set to replace. If, however, you have a complete base layer and only have the heart on layers above then you need to set it to combine. If the disposal is correct then check all of your layers for any inconsistancies such as stray pixels or even perhaps a blank layer as these could cause the flashing effect.
If you still cannot find the problem please upload the icon and I'll take a look at it.