One of the 64 short films (out of 7,000 submissions) at last month’s Sundance Film Festival was director Jeremiah Zagar’s mini-documentary, Heart Stop Beating, which tells the story of Texas Heart Institute surgeons Billy Cohn and Bud Frazier’s “continuous flow device”—an artificial heart that doesn’t beat, leaving the patient with no pulse.

“Cut out the whole heart, and replace it with two turbines,” Cohn explains.

The device was first used on a gravely ill 55-year-old Houstonian named Craig Lewis last March, with Zagar’s cameras in the operating room.

Watch below (but be warned that this is not for the squeamish):

The story is so incredible that one commenter on the film’s website wrote that her companion thought it was a sci-fi film until the final thirty seconds.

Unfortunately, as the film’s producers explained, there’s much more to the story:

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H/T to Eric Berger of the Houston Chronicle, who wrote about the heart and the procedure in an article last year, tracing the history all the way back to Michael DeBakey and Texas Heart Institute founder Denton Cooley’s early artifical heart projects. 

An exceprt from Cooley’s new memoir, 100,000 Hearts, can be found in the February issue of TEXAS MONTHLY.