How This 40-Year-Old Completed A 4-Mile Road Race Without A Human Heart

Although it took Randy Shepherd an hour and 40 minutes to finish a run in honor of war hero Pat Tillman last week, that race was still one of the biggest victories of the 40-year-old's life.

That's because Shepherd walked the course with an artificial heart powered by a 13.5-pound portable device he fit into his backpack.

Shepherd recently did an "Ask Me Anything" on Reddit about about life without a heart and how he completed that race.

While rheumatic fever weakened Shepherd's heart when he was a child, open heart surgery at 17 allowed him to be active for much of his adulthood. In recent years, however, additional heart troubles left Shepherd in need of a heart transplant.

Doctors removed Shepherd's heart last year and replaced it with the SynCardia Total Artificial Heart - a temporary heart for Shepherd as he waits for a human heart transplant.

The artificial heart saves the lives of victims whose two human heart ventricles can't pump enough blood. Replacing both heart ventricles and all four heart valves, the artificial heart allows for 9.5 liters of blood per minute to flow through each ventricle.

Shepherd participated in the April 26 4.2-mile Pat's Run in Phoenix, Arizona to help inspire others with severe health issues not to let their conditions stop them. Here's what he had to say in his recent Reddit AMA post.

The external Freedom® portable driver that powers Shepherd's artificial heart contains lines that connect to his body through his upper abdomen, requiring twice weekly cleanings to ensure the site doesn't become infected. The driver itself runs on two rechargeable batteries.

Shepherd has plenty of mobility because the heart's external driver is portable and the artificial heart doesn't require any electronics inside the body need to be fixed or replaced. During exercise, the artificial heart's ventricles can fill with 30% more blood to accommodate the body's greater movement.

Shepherd says his heartrate with the artificial heart is 135 beats per minute. The pulse is strong enough to feel a reverberation if one were to sit on a couch with him.

However, his heart rate does not increase with more exertion, which was one of the difficulties he faced when completing the walk.

There have been more than 400 implants of SynCardia Total Artificial Hearts since 2011.