A Dallas-bound Southwest flight was delayed Sunday after a human heart was discovered onboard that was meant to stay at a hospital in Seattle, officials said.
Flight 3606 had arrived in Seattle from Sacramento before taking off with the heart on board, the Seattle Times reported.
The captain turned the plane around in Idaho because it was "absolutely necessary to deliver the shipment ... as quickly as possible," the airlines said in a statement.
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Once on the ground in Seattle, the aircraft was taken out of service due to an unrelated mechanical issue, Southwest Airlines officials said. A new aircraft was brought in to continue the route to Dallas.
The issue caused a 5-hour delay for passengers.
"We sincerely regret the inconvenience to the Customers impacted by the delay, and we are following up with them with a gesture of goodwill to apologize for the disruption to their travel," Southwest Airlines said, in part, in a statement. "Nothing is more important to us than the Safety of our Customers and the safe delivery of the precious cargo we transport every day."
It wasn't immediately clear what the heart was for.
Southwest said the "life-critical cargo shipment" was for a hospital and had been sent by a company specializing in shipments. Parts of a heart, such as valves, can be recovered when whole heart transplants aren't feasible.
But no Seattle-area hospitals said they were involved. Organ-procurement organizations in Washington and California said they never use commercial flights for heart transplants.