98 Human Body Version 2.0 with artificial ‘respirocytes’ that would enable us to hold our breath for four hours or do a top-speed sprint for 15 minutes without taking a breath. Like most of our biological systems, our red blood cells perform their oxygenating function very inefficiently,  and  Freitas  has  redesigned  them  for  optimal performance. He has worked out many of the physical and chemical requirements in impressive detail. It will be interesting to see how this development is dealt with in athletic contests. Presumably, the use of respirocytes and similar systems will be prohibited from Olympic contests, but then we will have the specter of teenagers in junior high school gymnasiums routinely outperforming Olympic athletes. Freitas envisions micron-size artificial platelets that could achieve hemostasis (bleeding control) up to 1,000 times faster than biological platelets. Freitas describes nanorobotic micro- bivores (white blood cell replacements) that will download software to destroy specific infections hundreds of times faster than antibiotics, and that will be effective against all bacte- rial, viral and fungal infections, with no limitations of drug resistance. HAVE A HEART, OR NOT The next organ on my hit list is the heart. It’s a remarkable machine, but it has a number of severe problems. It is subject to a myriad of failure modes, and represents a fundamental weakness in our potential longevity. The heart usually breaks down long before the rest of the body, and often very prema- turely. Although artificial hearts are beginning to work, a more effec- tive approach will be to get rid of the heart altogether. Among Freitas’ designs are nanorobotic blood cell replacements that provide their own mobility. If the blood system moves with