A Southwest Airlines flight to Dallas had to turn around and return to Seattle yesterday. However, it wasn’t due to a sick passenger or a mechanical issue, at least not originally. It turns out that a human heart intended for delivery to a Seattle hospital had been left on the plane accidentally after a previous flight. Once the plane landed safely in Seattle, both the heart and the passengers were unloaded from the plane, which they then found had suffered an unrelated mechanical issue. Travelers were put on the next plane to Dallas after a five-hour delay.