Months into the COVID-19 pandemic, physicians still emphasize that key symptoms include a dry cough, fever, and shortness of breath — no surprise for a virus that infects the lungs.

Yet in the sickest patients, doctors keep finding collateral damage in the kidney, liver, and other organs.

A new Penn Medicine study suggests that in rare cases, the coronavirus can even stop the heart.

Among 700 COVID-19 patients at the Hospital of the University of Pennsylvania, nine suffered a sudden cardiac arrest after being admitted, the study authors reported Monday. Seven of the nine were under age 60.

While doctors managed to resuscitate six of those nine, including five of the under-60 group, the findings are a reminder that COVID-19 can cause injury throughout the body, senior author Rajat Deo said.

The cardiac arrests were among 53 cases of abnormal heart rhythm identified by Deo and his co-authors. Most, including all nine of the arrests, occurred in patients treated in the intensive care unit.

Evidence suggests these heart malfunctions are not the result of the virus’ infecting heart cells, said Deo, a cardiac electrophysiologist and an associate professor at Penn’s Perelman School of Medicine. Instead, they appear to occur when the immune system overreacts to the virus, leading to dangerous inflammation.

“When the body is under so much stress, just general, overt systemic stress and inflammation, then at that time, they’re just predisposed to arrythmias,” Deo said.

Eight of the nine cardiac arrests were “nonshockable,” meaning they were not the type that can be restarted with a defibrillator.

“That means CPR and medication, and you pray that the pulse comes back,” Deo said.

Some of the heart malfunctions may be the result of abnormal blood clots that can occur in COVID-19 patients, he and his co-authors wrote in Heart Rhythm Journal.

Yet one of the abnormal heart rhythms they identified — atrial fibrillation, typically abbreviated as A-fib — can itself lead to clots, so it can be difficult to disentangle what caused what. It is possible that some patients suffer from thrombosis — clotting — as a direct result of COVID-19 and also as a result of the COVID-19-induced heart malfunction, Deo said.

“If you have COVID-19 and A-fib, it’s sort of like a double thrombotic disease,” he said. “It’s a double whammy.”

Many of the patients who experienced heart malfunction while hospitalized already suffered from diabetes, high blood pressure, and other underlying conditions known to be associated with severe consequences from COVID-19.

The abnormal heart rhythms in Penn’s patients are consistent with what physicians have reported elsewhere, said Chad M. Colon, a cardiology fellow at the University of Alabama at Birmingham Hospital.

As at Penn, the arrhythmias at UAB Hospital are occurring primarily in the intensive-care ward, he said.

Colon, who was not involved in the Penn study, agreed with the authors that the heart malfunctions are not the result of the virus’ infecting heart cells, but of the patients’ overall sickness.

“This is probably more just a manifestation of their critical illness,” he said. “These patients are just uniquely challenging.”

Deo said the next step is to keep following patients who experience the abnormal heart rhythms to see if they experience any long-term harm.

With the number of cases resurging in some parts of the country, they likely will have no shortage of people to study.