The passengers on Southwest Flight 3606 were somewhere over Idaho Sunday when their captain came over the PA with a message: They were headed back to Seattle. That's because there was a "life-critical cargo shipment" that had been left on board, per the Seattle Times: a donated human heart. The heart should have been left in Washington after arriving from Sacramento, but instead it stayed on the plane and was Dallas-bound before the airline realized it hadn't been removed at Sea-Tac Airport.
CNN and its affiliate KTXL note that this heart wasn't intended for a full transplant; it was donated for its valves alone. That means a) it was in a thermally controlled box in the cargo hold, making it easier to forget, and b) it had, per KTXL, a "much longer transportation window" than if it had been intended for a heart transplant. Luckily, no damage came to it, and the heart got to where it needed to go on time, per the Sierra Donor Services nonprofit. The passengers, meanwhile, weren't too irked, as they were "happy to save a life," one man on board tells the Times. (Another organ donor was 107 years old.)