A 57-year-old American man who received the first ever genetically-modified pig heart is being closely watched as it remains unclear what will happen next.

The seven-hour experimental transplant on David Bennett took place at a medical facility in the US city of Baltimore. The transplant was considered the last hope for Bennett who was bedridden and diagnosed with terminal heart disease.

Doctors at the University of Maryland Medical Center note that the transplant marks the culmination of years of research and could change lives around the world.

Surgeon Bartley Griffith believes using animal organs for so-called xenotransplantation could bring the world a step closer to solving the organ shortage crisis. Pig heart valves are already being used.

In October last year, New York surgeons successfully transplanted a pig’s kidney into a person. The recipient of that experimental transplant was brain dead with no hope of recovery.