While a courier for LifeNet waited for pickup in Seattle, the tissue was left behind, just like a suitcase. On Sunday afternoon, a Southwest Airlines flight bound for Dallas made a hairpin turn over eastern Idaho and headed back for Seattle-Tacoma International Airport. Someone forgot to unload the heart before the plane left for Dallas, and the captain announced over Idaho they were turning back.  (CNN) A Southwest flight was forced to turn around after a human heart meant for donation was accidentally left on board, the airline said.  Please enable Javascript to watch this video 
 
 SACRAMENTO — Southwest Airlines says a Dallas-bound flight returned to Seattle last weekend because a human heart was left onboard. That’s where LifeNet Health Inc. was set to remove the valves for a future surgery. Southwest flight 3606 landed at Sea-Tac after about three hours in the air, and the “life-critical cargo shipment” was unloaded from the plane, Southwest spokesman Dan Landson said by email. He added that Southwest made the decision to return because it was “absolutely necessary to deliver the shipment to its destination in the Seattle area as quickly as possible.” 
 
 “Nothing is more important to us than the safety of our customers and the safe delivery of the precious cargo we transport every day,” Landson said. After a five-hour delay, the passengers once again took off for Dallas.
– 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.)