The wound killed him, simple as that. The stingray barb, an eight inch blade of serrated cartilage. It went straight into his heart. A blade in the heart is a blade in the heart. Pulling it out was a desperate move, maybe even a reflex. But it wouldn’t have mattered whether they left it in or not. The damage was done the second it pierced the heart muscle – A big trauma like that is an uncontrollable bleed, he was bleeding out from the inside.
Pulling it out could have bled him worse sure. I guess it would be like pulling a cork from a bottle. But the bottle was already shattered – The man was on a boat, miles from any surgeon who could have plugged the hole. And nobody can just plug a hole like that on a boat deck, he had no chance, over before he knew it.