I have to take beta-blockers (bisoprolol) and one drug lowering blood pressure (ramipril). I had an acute myocarditis in july and will take the drugs until october.
The lowered heart rate could boost freediving performance, but there's another, potentially more important aspect: relaxation. With beta-blockers, you just don't get that excited, and this could be very helpful during competitions. There's a reason why racing drivers used to take beta-blockers
The doctors told me to avoid freediving and heart rates above 100 for the next 3-6 months. I keep freediving though, just for the joy of it; nothing deep, fast or performance-driven. Last week I had my first pool training session since my heart issue occured back in july 1st. As a biochemistry phd and pharmaceutical researcher I was curious to see what the beta-blocker would do to my freediving. WOW that was one of the most satisfying training sessions in years! One of my exercises is to take a 1min break on the pool's floor at 5m, then dive 2 laps of 22m each. Now I easily rested 2minutes before diving the 2 laps! Contractions came much later, I was so relaxed and comfortable i felt i could fall asleep at 5m! I easily did 3'45'' of very slow dynamic. I didn't do greater distances or faster dives in order to avoid my heartrate hitting 100bpm. But the feeling was great!