Perhaps this could explain higher rates of heart attacks in scuba than in other sports? But only if you are cold. I am more interested in the effect of the higher pressures on the body at depth which is not much in the above test in a swimming pool at shallow depths.
Are there higher rates of heart attacks in scuba than in other sports? I have not seen those statistics.
If there is a higher rate (and there could be), another reason could be that scuba tends to attract an older population for several reasons. In my younger days, I was a basketball coach and player, a volleyball coach and player, a soccer coach and player, and a citizen ski racer. I don't do any of those activities any more, in large part because of the toll those activities took on my body. When I was planning for one of my knee surgeries, I asked the orthopedist when I could get back to full activity, and when she gave me a date in the fall, I said, "Great, because I have to register for the ski racing season by next week, and I wanted to be sure I would be ready." She asked, "You race on those knees?" I said, "Yes, I do." She said, "No, you don't."
My son was an avid soccer player playing in a number of adult leagues, but he has given it up for the same reason and is looking for a less punishing activity to replace it. For me, the less punishing activity I sought out as I aged was scuba. My aching knees loved the effortlessness of diving.
It is very possible that I may some day have a heart attack while diving. I did not have a heart attack while playing those other sports, but the reason would not have anything to do with those sports being less demanding of my heart functions.