The heartbeat is synonymous with human life, but could we possibly live without one? Flatline tells the extraordinary story of Dr Bud Frazier and Dr Billy Cohn of the Texas Heart Institute, who in March of 2011 performed a continuous-flow artificial heart transplant to extend the life of a dying man. In doing so, they proved that it was possible for a person to live without a pulse. Directed by the US filmmaker Jeremiah Zagar, this short documentary explores how some advances in medical science and technology brush up against the limits of what we view as possible, making us reconsider what it means to be human.