As the coronavirus pandemic develops, researchers are getting a better picture of the long-term problems that the virus can cause after people recover. Now, two studies from Germany argued that COVID-19 can have a severe effect on the heart, even when the illness wasn’t severe.

People with underlying cardiovascular problems such as high blood pressure and coronary artery disease were known to be at higher risk of infection and death since the pandemic began. Doctors connected pulmonary embolisms, strokes, and heart attacks with the virus. However, the connection between COVID-19 and heart problems may extend far beyond this.

A study from the University Hospital Frankfurt looked at the cardiovascular MRIs of 100 people who had recovered from the coronavirus and compared them with heart images of people who hadn’t been infected.

Most of the patients hadn’t been hospitalized and recovered at home, with symptoms ranging from none to moderate. Two months after recovering from COVID-19, the patients were more likely to have troubling cardiac signs than people in the control group. Up to 78% of them had structural changes to the heart, while 76% had evidence of a biomarker signaling cardiac injury typically found after a heart attack, and 60% had signs of inflammation.

“This means that the heart is involved in a majority of patients, even if Covid-19 illness does not scream out with the classical heart symptoms, such as anginal chest pain,” Valentina Puntmann, who led the study, told STAT. “The relatively clear onset of Covid-19 illness provides an opportunity to take proactive action.”

Meanwhile, another recent study looked at the autopsies of 39 people who died last year when the pandemic started with an average age of 85.

The results showed high levels of the virus in the hearts of 24 patients, with the researchers calling for further studies on the long-term consequences of the novel coronavirus.

The two studies suggest that Covid-19 could lead to heart failure, a progressive condition that reduces the ability of the heart to pump blood throughout the body.

While it’s still too early to tell if the heart damage in patients recovering from the novel coronavirus will be permanent or transitory, cardiologists are concerned.

“These are two studs that both suggest that being infected with Covid-19 carries a high likelihood of having some involvement of the heart. If not answering questions, they prompt important questions about what the cardiac aftermath is,” Matthew Tomey, a cardiologist at Mount Sinai Health System not involved in the studies, told STAT.

More than 16 million confirmed cases have been reported worldwide, according to data from a Johns Hopkins University tracker.

Of those infected, more than nine million have recovered from COVID-19 globally. Positive cases have recently begun to rise again in Europe, subject to the second wave of cases.

Clyde Yancy, a cardiologist at Northwestern’s Feinberg School of Medicine, and Gregg Fonarow, a cardiologist at UCLA’s Geffen School of Medicine, wrote an editorial about the two recent studies on heart problems related to the novel coronavirus and called for more research into the problem.

“If this high rate of risk is confirmed, … then the crisis of COVID-19 will not abate but will instead shift to a new de novo incidence of heart failure and other chronic cardiovascular complications,” they wrote. “We are inclined to raise a new and very evident concern that cardiomyopathy and heart failure related to Covid-19 may potentially evolve as the natural history of this infection becomes clearer.”

Both the study that looked at MRIs and the one that looked at autopsies were published in the journal JAMA.