The Four Noble Truths is in the realm of the conventional truth and the Heart Sutra is in the realm of the ultimate truth. And it's vital for us to understand the ultimate truth for attaining enlightenment. The source of all sufferings is separation between oneself and others. So, we need to transcend duality and throw away all notions in order to stop the separation. For that, wisdom of emptiness (interdependent co-arising) is essential. Emptiness (interdependent co-arising) means two sides of the same coin (all pairs of opposites are "not two", but "not one"). If one side arises, the other side arises at the same time. If one side is removed, the other side is also removed at the same time. Therefore, it is no exaggeration to say that emptiness (interdependent co-arising) is the ancient "general theory of relativity" and "cognitive therapy".
Regarding non-duality, the following material is just for your reference. http://www.slideshare.net/compassion5151/light-and-darkness
Tulips Photo by Joel Bramley