Two doctors at the Texas Heart Institute in Houston had a big breakthrough this spring, giving a near-dead man a new kind of artificial heart that extended his life, but removed his pulse. After using the pulseless heart on 38 cows, Dr. Billy Cohn and Dr. Bud Frazier swapped one in for Craig Lewis' defunct heart. Lewis died a month later from other causes, but his heart pump worked flawlessly, the doctors say. Here, a brief guide:

Where's the pulse?
Cohn and Frazier cobbled together their artificial heart using two ventricular assist devices (VADs) that move blood through the body using a continuously whirring rotor, not a pulsating pump. Some studies show that these VADs last longer than traditional heart pumps, because there is only one moving part, the rotor. But the effect is a little creepy. Pointing at a healthy test calf, Cohn says: "If you examined her arteries, there's no pulse. If you hooked her up to an EKG, she'd be flat-lined.... By every metric we have to analyze patients, she's not living."

This is a new technology?
Not exactly. VADs to augment one side of the heart, usually the left, have been around since the 1980s, although they have gotten smaller and better over the years. The controversial idea that humans don't need a pulse got a boost in 2010, when former Vice President Dick Cheney got a continuous-flow HeartMate II pump to replace his left ventricle, killing his pulse (and prompting numerous jokes). In connecting two modified HeartMate II's to replace the entire heart, "what we've kind of done is taken two motorcycles, strapped them together, and called it a car," says Cohn.

Is this the future of heart transplants?
Cohn and Frazier are convinced of it. Unlike other heart replacements, "these pumps don't wear out," Frazier says. "We haven't pumped one to failure to date." Cohn says most researchers are too focused on trying to recreate the pulse, because all animals have one. If you remove the pulse "from the system, none of the other organs seem to care much." Ditching the heartbeat is a textbook "game-changing paradigm shift," says Donna Cicotte at her blog. It's like when the Wright brothers came up with a new way to fly that didn't try to mimic flapping wings. 

What are the main obstacles?
Powering the pumps, for one thing. Currently, Cheney and the thousands of other single-VAD recipients carry around a heavy, awkward battery pack that connects to the pump via an easily infected wire that feeds through the abdomen. Luckily, an engineer and heart surgeon have just unveiled a prototype of a wireless power pack for heart pumps, says The Economist. So prepare for "thousands more healthy, active ex-politicians without a heartbeat. Insert your own punchline here."

Is there anything dehumanizing about losing your pulse?
It certainly raises some tricky questions, says Ryan Brower at his blog. "If you don't have a heartbeat are you just a human-robot?" Well, most "pulseless patients feel nothing unusual," says Lawrence Altman in The New York Times, although it must be odd "to wear bracelets or other identifications to alert emergency room doctors as to why they have no pulse." Losing "the familiar, primordial sound of a beating human heart" is definitely a tradeoff, says Carrie Feibel at NPR. But at least for Cohn and Frazier, "that's a small, poetic price to pay to make medical history."

Sources: NPR, Discovery News, Houston Chronicle, Economist, Texas Heart Institute, New York Times, Humanrobots, Donna Cicotte