Even though it’s known as a respiratory virus, doctors believe the coronavirus can directly infect the heart muscle and cause other problems leading to heart damage.
In some people, as Covid-19 decreases lung function, it may deprive the heart of adequate oxygen. Sometimes it causes an overwhelming inflammatory reaction that taxes the heart as the body tries to fight off the infection.
The virus can also invade blood vessels or cause inflammation within them, leading to blood clots that can cause heart attacks.
Clots throughout the body have been found in many Covid-19 patients. That has led some doctors to try blood thinners, although there is no consensus on that treatment.
Dr Sean Pinney of the University of Chicago says people with heart disease are most at risk for virus-related damage to the heart. But heart complications also have been found in Covid-19 patients with no known previous disease.
A recent review in the Journal of the American College of Cardiology notes that evidence of heart involvement has been found in at least 25% of hospitalised coronavirus patients. At some centres, the rate is 30% or higher.
Some studies have found elevated enzyme levels and other signs suggesting heart damage even in patients with milder disease. It is not known whether that damage is permanent.
One small study found evidence of the virus in the hearts of Covid-19 patients who died from pneumonia. Another, using heart imaging, found inflammation of the heart muscle in four college athletes who had recovered from mild Covid-19 infections. There were no images available from before the athletes got sick, and therefore no way to know if they had pre-existing heart problems.
Dr Tom Maddox, an American College of Cardiology board member, says it's unclear if the virus can cause a normal heart to become dysfunctional.
“There’s still so much we don’t know," Maddox said.