This article was taken from the March 2015 issue of WIRED magazine. Be the first to read WIRED's articles in print before they're posted online, and get your hands on loads of additional content by subscribing online.

Your heart beats 100,000 times every day, pumping 5.6 litres of blood around your body every 20 seconds. Place two fingers on your wrist: that pulse that you feel is your blood stopping and starting as it moves through your arteries. Your pulse is living proof that you're alive. Or is it?

Billy Cohn and Bud Frazier, two cardiac surgeons at the Texas Heart Institute in Houston who have spent their careers developing devices to replace or assist failing hearts, are out to prove that wrong. The heart doesn't have to pump, they believe -- it would be far more durable as a mechanical propeller that pushes blood in a continuous flow around your body. Their invention, an artificial heart, does just that.

The pair transplanted their pulseless artificial heart into 70 bovine calves. The animals all showed a flatline on an EKG, but remained alive and well. In March 2011, the team tested a prototype in a human patient, 55-year-old Texan Craig Lewis, who was suffering with amyloidosis, a rare autoimmune disease. Lewis lived for six weeks with the heart installed, but had to be unplugged when his kidneys and liver failed due to the condition.

Their latest version of the heart -- a fist-sized plastic device with two blades on either side of the rotor -- is currently being developed with Australian engineer Daniel Timms and, like its predecessor, is being tested in calves. "The device is still pre-clinical, and not for use in human patients, but this may change next year," says Timms. Should human trials be successful, a flatline may one day be a sign of life.

This article was originally published by WIRED UK