We do have two hearts, one for venous (low pressure) flow and one for arterial (high pressure) flow. Also, each "heart" has its own secondary pump as an additional failsafe mechanism. This is the reason why heart defects or acquired issues can go undiagnosed for several years while the individual still maintains a healthy function.

You can argue that you have at least 3 brains: left and right hemispheres, and the cerebellum. Specialization gives these 3 structures functions and architectures that blur their independence from their counterparts. Damage to any of these structures can be compensated by the others but, of course, the level of compensation varies between individuals and age.

The digestive system is a completely different story because of how embryonic development works. We (and most animals) develop around a whole that becomes our single digestive tube (or tract). We are basically worms with funny looking appendages with wiggly tiny tentacles at their ends.