The Shrivatsa represents the Buddha's heart, the essence of Bodhicitta, which means the "awakened mind" or "universal compassion".
"In its endless configuration, it aims to evoke Samsara, the cyclic nature of life, death and rebirth without beginning or end"
It can also stand for karmic consequences: pull here, something happens over there. And is an apt symbol for the methods of Vajrayana: often when we tug at one part of a knot while trying to loosen it, another part gets tighter. Sometimes, you have to work with the knot, to get it to come undone. And lastly, it expresses the intricate interplay and interaction of the opposing forces in the dualistic world of manifestation, leading to their union, and ultimately the harmony of the universe.