he was a BN in the 1970s, then had a yacht management business in RI.
He was my poster boy for for fitness. When his son started playing soccer, he became a coach and was largely responsible for organizing the local soccer fields.
He was still in demand on racing yachts. He was prepping a boat that had just been launched and spent most of the day aloft. He came down from the rig late afternoon, made it to the companionway, collapsed on the cabin sole, and never revived.
He was 50 with, as far as I know, no history of heart problems.
Years later, I surmised he might have succumbed to deep vein thrombosis . . which I guess is similar to what you are describing.