Redundant human hearts

I was looking at a cool website called www.longbets.org in which people make predictions for the future (around 10-100 years). I had an idea for a "longbet" - my own prediction on the future but when I went to enter it, they asked for a $50 publishing fee. I found it a lower cost to publish in my own blog instead. So here is my prediction: What is your prediction? In 30 years, some humans will have an additional heart installed as insurance for a heart attack or pulmonary failure. During cardiac arrest, the second heart will keep them alive until medical intervention repairs or transplants the primary heart. Why? Provide an argument in favor of your prediction: RAID5 hard disk systems have provided a popular layer of reliability for mechanical hard disks which always fail eventually. Why not do this for biological reliability? (Of course this will create huge ethical issues because there won't be enough spare hearts for everyone to have one... but that's a separate issue.) What do you think?