Sadly, it does happen. I knew an Air Force Colonel, early 40s, physically fit and near the lower end of the insurance “weight tables” for his height. Always in the gym or doing PT at 6 am. Finished a workout one morning at Langley AFB, went straight to his desk. When he failed to show up for a nine am staff meeting, someone was sent to check on him. Didn’t respond to a knock on his door, so the Lt went into his office. Found the Colonel face down on his desk, dead of a heart attack.
I also remember a Lt Col (navigator) from my days in SAC. Retired in early 85 after 20 years of active duty. Had just built his dream home and landed a job with a defense contractor. Died from a heart attack two weeks after his retirement ceremony. He was 43.
I'm sure more guys had heart attacks on the ship likely while in port. The chief that died during the deployment we were on was taken in a body bag to the aft walk in cooler and a watch posted outside. This would be protocol for anyone who died onboard by accident or any other circumstance otherwise. My shop which was Air Conditioning & Refrigeration had the responsibility for standing that watch until fly off was arranged.
Heart attacks are not a respector of ones age or youth. My first wife had a fatal one at age 23.
When I was stationed in Germany, our brigade surgeon had a massive stroke and died a day later. I can remember that he was a health nut, and could PT anyone of us into the ground.
Then while I was stationed at Ft Polk, we had a guy in my unit drop dead during PT. According to the doctors, he was dead before he hit the ground.
Both cases they were in their early to mid 40’s