SEATTLE (AP) — Southwest Airlines says a Dallas-bound flight returned to Seattle last weekend because a human heart was left onboard.

The flight arrived in Seattle from Sacramento. Someone forgot to unload the heart before the plane left for Dallas, and the captain announced over Idaho they were turning back.

The heart was being sent to a tissue processor to recover a valve for use in a future transplant. We’re told the delay did not impair the heart’s usefulness.