The trick is practise and of course the art of steaming milk. The espresso crema is not as important as some may think for the purpose of pouring a heart, the art is in the milk. If you're not able to pour a heart, you need to recheck your steaming process.
Here's a picture of the end result!
Take a look at the video below and take note of the consistency of the milk. It's Latte Art, not Cappuccino Art so make sure you are steaming the milk, not frothing the milk. Also, the milk should be steamed to be warm to the touch, not hot to the touch. I hope this can get you one step closer to perfecting this art.