5-chambered hearts

The process of animal evolution is predictable. We understood that the gravity has been increasing and animals in order to better overcome this high gravity have been forced to build themselves stronger hearts: one-chambered, two-chambered, three-chambered and finally four-chambered hearts. As we know, the largest and the most successful animals at present are those who have 4-chambered hearts (e.g. Mammals and Birds). We also understand that the increase of gravity is now continuing. It is clear that the 4-chambered heart, too, in near future, will lose its power of overcoming the gravity and the animals will have to build stronger hearts. That is the question: Are animals thinking of building stronger hearts? Have they taken measures about this? Which method they will use to strengthen their blood-circulation system? As consequence this final question arise: among Mammals, which species have the high chance of reaching a powerful blood-circulation system? After the evolution oftheir blood circulation system, will they remain Mammals? Or will they find a new class of animals? What other characteristics will they have?