The Northern California woman who is the first known person to die of covid-19 in the United States passed away from a massive heart attack brought on by the disease, according to an autopsy report published Saturday by the San Francisco Chronicle.

Patricia Dowd, a 57-year-old from Santa Clara, Calif., died on Feb. 6 after fighting flu-like symptoms for several days. The Santa Clara County medical examiner described her as “mildly obese,” but didn’t indicate any underlying health conditions that would have made her vulnerable to severe infection.

Traces of the coronavirus were found in her heart, trachea, lungs and intestines, according to the report posted by the Chronicle. She died from inflammation and rupturing in her heart, the medical examiner concluded.

“There’s something abnormal about the fact that a perfectly normal heart has burst open,” forensic pathologist Judy Melinek, who was not involved in the autopsy, told the Chronicle. “The heart has ruptured. Normal hearts don’t rupture.”

Much remains unknown about how the coronavirus works and why it affects some people more severely than others. Experts initially believed it primarily attacked the lungs, but they’ve since seen evidence that it can ravage nearly every major organ in the body, causing strokes, liver damage, acute kidney disease and other life-threatening problems.

The virus is especially threatening to people with heart disease. The massive inflammation caused by covid-19 can trigger fast, abnormal heart rhythms, leading to heart failure and death, even in patients who aren’t experiencing chest pains or shortness of breath.

Until last week, health officials believed the United States’ first coronavirus death occurred Feb. 29 in Kirkland, Wash., an early epicenter of the American outbreak. Last Tuesday, officials in Santa Clara revealed that tissue samples taken during autopsies of two local residents who died at home earlier in the month tested positive for the virus.