Have not tried on hard core but makes zealot mode a walk in the park.
Oh and SPOILERS
Use the pulse rifle. I'm sure you can use w/e weapon you want but I prefer the PR. As soon as the fight begins unload into Nicole and then the heart when its exposed. As soon as the marker closes on the heart turn 90 degrees either left or right and start running. You want to run a path around the edge of the thing your on and get all the enemies chasing you. When you first start your run you will need to dodge a little as they spawn but once all of them have spawned and started the chase you'll be fine. Once your confident there all behind you can reload while running and then turn around and use the PR alt-fire or just spray into them, don't spray too long or they will get too close. Turn back around and run some more, turning and firing when you feel safe until only Nicole is left. Note where the marker is and unload into Nicole and then the heart when its exposed. Repeat the process. I only had to unload into the heart 3 times to kill it.
Hope this helps anyone having trouble with the final boss.
Life should be like an MMO. Going to work should mean stepping outside and killing boars for gold.