There’s powerful evidence that COVID-19 affects the heart and not just the respiratory system. Experts are seeing more recovered patients with inflammation and scar damage in their hearts and are encouraging people who have been sick for more than a few days to ease slowly back activity but not into vigorous activity. Athletes are advised to get a blood test and an EKG, or electrocardiogram, before resuming sports.

“You don’t get sick with COVID-19 and stay home from school for a week and then go back and play two hours of soccer,” Dr. Steven Erickson, a sports medicine specialist from Phoenix, Arizona told USA Today, adding that athletes should be symptom-free for two weeks before getting back into the game.

A study published by Ohio state University found that four out of 26 competitive athletes who had COVID-19 had symptoms of myocarditis, a disease which affects the heart muscle and can cause heart failure or sudden death, according to USA Today.

“It is believed that there are many organs of the body that are affected by the virus,” said Chris Glembotski, Ph.D., a renowned researcher in cardiovascular disease at the University of Arizona. “After infection, the virus goes to different organs and tissues and after entering them causes and inflammation response.”

Research using stem cell technology confirms that Sars-CoV-2, the virus that causes COVID-19 not only infects the lungs but can impact heart cells as well. In lab experiments, researchers found that the virus infects heart cells by attaching itself to ACE2, the receptor it uses to invade human cells. It not only infected the heart cells, it caused them to beat irregularly.

Co-author Clive Svendsen, professor of Medicine and Biomedical Sciences at Cedars-Sinai, said in a news release:

“While this could be the result of massive inflammation in response to the virus, our data suggest that the heart could also be directly affected by the virus in COVID-19.”

Glembotski says COVID-19 patients should proceed with caution, according to USA Today.

“Most of what we are learning about COVID-19 is from research emerging currently, so not a lot is known. There’s more to be found out.”