As far as flight delays go, this was a tough one to gripe about. Early Thursday morning, Southwest Airlines Flight 3606 turned around in midair, halting its trip to Dallas to return to Seattle. Among the plane’s cargo was a human heart—whoever had ordered it sent from Sacramento didn’t realize they were missing a cooler covered in biohazard stickers until the plane had left Sea-Tac airport and was a third of the way to Texas. And so the pilots booked it back to the Emerald City. But here’s where the story gets weird: According to the The Seattle Times, no hospitals in the region were awaiting the wayward organ.

Who was the owner of this lonely heart? How did it wind up flying commercial and suffering the fate of so many a lost bag? Transplant organs are precious commodities that require surgically precise logistics to get from bodies that deed to bodies in need. The flight from Sacramento to Seattle alone would have been pushing the time limit before the heart was no good, and that’s not counting travel to and from the airport, boarding, taxiing, and the potential for delays. It’s almost like whoever shipped it to Seattle had never intended for this heart to beat again.

Bingo. “There was no intended recipient,” says Deanna Santana, public relations manager for Sierra Donor Services, the organ procurement organization that sent this heart from Sacramento to Seattle. “We were not functioning as an organ procurement, we were functioning as a tissue recovery for heart valves, which were to be sent to a tissue processor,” she says. This might sound like a superficial distinction, but when it comes to transplants, it’s the difference between life or death.

Owner of a Donor Heart

If you recall middle-school biology, tissues are collections of identical cells all doing the same job. Organs are collections of tissues working in concert for some sort of more complex function: Hearts pump blood, lungs add oxygen to blood, kidneys remove toxins from blood, and there are a bunch of others performing various blood- and non-blood-related jobs. Because organs are so complex, they have to be recovered from a living body. But, for obvious ethical (not to mention legal) reasons, that living body must be brain-dead.

“The organ procurement process starts when somebody in a hospital has a body that’s bleeding out, but their brain is already gone,” says Scott Perry, an independent transplant coordinator based in Pittsburgh. Under federal law, any hospital that receives funding from the Center for Medicare and Medicaid Services (which is most hospitals) has to contact their local Organ Procurement Organization whenever a patient meets these conditions. (Sierra Donor Services is one of the 58 nationwide organ procurement organizations.) This sets the organ donor process into motion.

The first thing these organizations do upon contact is check whether the patient has any medical conditions, such as cancer, that might disqualify them as a donor. If it’s all clear, the organ procurement organization contacts the family to get consent (or, if the deceased had signed an organ donor form, inform the family of their choice). Once that’s settled, the organ procurement organization sets about finding a suitable recipient. They do this by plugging the organ’s information into a computer system called DonorNet, which contains details on every person needing an organ in the US. DonorNet’s algorithm ranks potential recipients on a number of factors, like geography, blood type, medical urgency, and organ size—a preteen’s lungs won’t work in an adult’s chest, for instance. One important note: DonorNet generates a unique list for every organ, and its parameters are always changing to make organ distribution more fair, equitable, and inclusive.