An organ donor services organization is re-evaluating its protocols after a human heart being flown to Seattle on Southwest Airlines was left on board the plane.Instead of being removed from the cargo hold in Seattle, its final destination, the donated heart valve tissue was left on the plane by accident. It’s a situation many frustrated flyers have faced with lost baggage, but a minor inconvenience escalates to a grave situation when it happens with donated organs.The heart valve tissue was packed on ice and taken from a courier at Sacramento International Airport (SMF) on Sunday and flown to Seattle (SEA) on Southwest flight 3606, which landed at SEA at 2:15pm. Baggage handlers mistakenly left the carefully packed box in the aircraft cargo area, and flight 3606 took off at 3:02pm for its next destination, Dallas. It wasn’t until more than an hour into the Dallas flight that the pilot turned the plane around to deliver the heart back to Seattle, causing a five-hour delay for the passengers heading to Dallas Love Field (DAL). FlightRadar24 shows the pilot making a U-turn over southeastern Idaho.“Everybody involved is going to evaluate the process, they’re going to make sure what happened and make sure this doesn’t happen again,” Deanna Santana of Sierra Donor Services, which organized the valve donation, told CBS News Sacramento. “It’s very clearly labeled that this is a gift. It’s clearly labeled that this is human tissue for transplant so that the handlers are aware to treat this very carefully.”The donor’s family was kept apprised of the delay.Southwest confirmed that the heart tissue was left on the plane. “During Flight #3606 with scheduled service from Seattle to Dallas this past Sunday evening, we learned of a life-critical cargo shipment onboard the aircraft that was intended to stay in Seattle for delivery to a local hospital,” Southwest said in a statement to TPG. “Therefore, we made the decision to return to Seattle to ensure the shipment was delivered to its destination within the window of time allotted by our cargo customer.“Sign up for our daily newsletterEmail addressSign upI would like to subscribe to The Points Guy newsletters and special email promotions. The Points Guy will not share or sell your email. See privacy policy.The airline also said that once on the ground in Seattle, the plane had to be taken out of service due to a separate maintenance issue, prolonging the delay for its Dallas-bound customers. Southwest has apologized to those passengers and offered them a “gesture of goodwill.” “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’s statement continued.Luckily, this story has a happy ending. As heart valve tissue has a 48-hour travel window if properly stored, the pilots were able to deliver the heart in the nick of time. It landed back in Seattle at 5:56pm, having lost more than three and a half hours on the detour to Dallas.This post has been updated to clarify that the donor’s family was alerted about the delay, not a recipient’s family.