An overactive heart chakra might have 2 effects : one positive, which is that you won't have any difficulty to manipulate it and feel the energy inside it, but one negative which is that it might withrdraw your attention from the real goal if you got too much sensations. I suggest you to work on you other chakras to balance your energy body, and the overactive chakra will display less sensations after, although it would still be one of your most active chakras.
On the other hand, an overactive heart chakra after some first stimulation with NEW can indicate that it was blocked and the blockages ar being removed. Then it won't help you more with the healing. My advice is : just test and see if the healing works fine :)
I have a very overactive Heart Chakra. Would this be good or bad if I wanted to learn to heal as Robert Bruce described in his article?