Previous parts here:
Creating a scientifically semi-valid super-soldier, part 1: Skeleton
Creating a scientifically semi-valid super-soldier, part 2: nervous system
Creating a scientifically semi-valid super-soldier, part 3: Physical shock resistance
Creating a scientifically semi-valid super-soldier, part 4: respiratory system
And one thread that has some information that is helpful: Is a double circulatory system useful?
In some sci-fi or fantasy, when they want you to know that some kind of creature means business they give them extra hearts. If you get an extra heart you have a spare one if the other one gets damaged, right? Often this goes along with some kind of super-coagulant that lets blood clot almost immediately, somehow without generating super-thromboses.
So the question is, how could you create an enhanced being that won't keel over if its heart is hit? This includes the circulatory system (might need a separate question later). The body should be able to build, maintain and repair this system.
I had two ideas on possible systems. The first is a lot like described in the "double circulatory system" thread linked above. Two hearts, each has a small circulatory system to one lung half (in case of an enhanced being with bird-lungs, two lung areas will be used). Then they pump it into the body. To preserve redundancy potential, the blood vessels each reach most of the body but each from the other end. So the right heart does the top of the arms for example before going to the bottom of the arms. If the right heart fails, the left heart will still supply enough blood to keep the top of the arms alive and slightly functional.
A big problem with such a system would be blood pressure. The blood vessels would need to be thinner because each heart pumps less blood per unit time and because they would take up too much space otherwise. This means that the blood quickly loses its velocity through your veins and needs to use your lymph system and muscle-pumps (normal contraction of the muscles pushes blood out and further).
Another option I thought off that could coincide with many systems, would be a peristalsis-capable blood system. This has two advantages. Even if the main heart stops the blood vessels would be able to pump the blood further, and in case of a blood vessel rupturing there is little need for high-strength coagulant if the blood vessel itself can squeeze shut and prevent further blood loss. The big drawback is, of course, the large amount of energy such a system would need.
So what would be good and solid options for a heart and circulatory system to work on an enhanced super-human or similar?