In regard to cardiac deaths among athletes, this is really just fear-mongering among those resisting covid vaccination:
"Sudden cardiac death (SCD) is the most frequent medical cause of sudden death in athletes, and estimates vary widely based on the population. A recent estimate of SCD incidence ranged from 1 in 40,000 to 1 in 80,000 athletes per
year.12 Though SCD is rare, its occurrence in athletes who are often young and presumably healthy has a large emotional and social impact on the surrounding community." - 2016 paper, Methodist DeBakey Cardiac Journal
Closer to home, the 2007 Comrades, for instance had 2.5% of the male entrants suffer heart attacks. Heart attacks are just not that uncommon among athletes, and the stress of professional level physical exertion will result in underlying heart problems presenting as acute.
Bottom line? This, like so much anti-covid vaccination propaganda, is fundamentally dishonest. An honest statistic would be to compare pre covid vaccination SCD death rates among athletes with post vaccination rates. But honesty has not been the hallmark of this debate, on either side.