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SEATTLE -- A Southwest Airlines flight from Seattle to Dallas turned around Sunday when the crew learned a human heart intended for a hospital was left on the plane.



Flight 3606 was en-route to Dallas when the crew learned the heart was onboard, a Southwest Airlines official told Q13 News. The crew quickly turned around in order to get the heart to the hospital.



The story was first reported by The Seattle Times.



"We made the decision to return to Seattle as it was absolutely necessary to deliver the shipment to its destination," a spokesperson for Southwest Airlines said.



Once on the ground, the flight was taken out of service due to an unrelated mechanical issue. Another plane was brought in, and passengers took off again.



All-in-all, it was a five-hour delay, the spokesperson said.



"We sincerely regret the inconvenience to the customers impacted by the delay," the spokesperson said. "Nothing is more important to us than the safety of our customers and the safe delivery of the precious cargo we transport every day."



Southwest planned to offer a "gesture of goodwill" to all those onboard.



The Seattle Times posted an article on Thursday that said the heart was being sent to a tissue processor in order to recover a valve. Click here to read more from the Times.