Study finds cardiac problems in pro athletes who battled COVID-19 are RARE as less than 1% had heart inflammation after being infected A new study funded by the NFL, MLB, WBA, NBA, NHL, and MLS has found that heart inflammation is rare in pro athletes who had mild COVID-19 symptoms Experts say the results aren't definitive and more outside research is needed Of the nearly 800 professional athletes who were studied, less than one percent suffered from heart inflammation after overcoming the coronavirus They were sidelined for about three months and returned to play without any problems, said Dr. Mathew Martinez of Morristown (New Jersey) Medical Center