A human heart left on a commercial airliner provides a glimpse into the nation’s transplant system, which relies on an obscure network of nonprofit organizations to collect and transport human organs and tissue.

The heart traveled in the cargo compartment of a Southwest Airlines flight from Sacramento to Seattle on Sunday. It was supposed to be picked up in Seattle but remained on the plane when the aircraft left for Dallas. There are conflicting accounts of what went wrong, and an investigation is underway.

Southwest realized the problem about 90 minutes into the flight to Dallas. The pilot issued an announcement to passengers, made a hairpin turn and headed back to Seattle.

Passengers were at first confused, then generally supported returning to deliver the heart, in case it was needed to save a life, one passenger, Andrew Gottschalk, has told media outlets.

As it turned out, the heart was headed to a “tissue processor” in Renton, Washington, a suburb of Seattle, where the valves could be removed for transplant, according to an official with LifeNet Health, a nonprofit organization in Virginia Beach that runs the facility. Tissue processors prepare heart valves, skin, bone and other body parts for use in medical procedures.

Initial testing indicates no damage to the valves, which have been removed, said LifeNet Vice President Doug Wilson. “They are in high demand, so they will likely be transplanted as soon as that testing is complete,” he said.

Sen. Todd Young, R-Ind., said Friday that the incident “strikes me as another example of a need for more oversight of the entire organ donation system.”

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