The Santa Clara woman whose death from COVID-19 is the earliest so far known in the United States suffered a massive heart attack caused by coronavirus infection, signs of which were found throughout her body, according to an autopsy report obtained exclusively by The Chronicle.

Patricia Dowd, 57, died Feb. 6 and had reported flu-like symptoms in the days before her death, according to the report. The autopsy, performed by medical examiner Dr. Susan Parson, found COVID-19 viral infection in her heart, trachea, lungs and intestines.

“There’s something abnormal about the fact that a perfectly normal heart has burst open,” said Bay Area forensic pathologist Dr. Judy Melinek, who was not involved in the autopsy but read the report at the request of The Chronicle. “The heart has ruptured. Normal hearts don’t rupture.”

“This heart ruptured or tore open because of an infection of the heart muscle caused by the coronavirus,” Melinek said.

Parson’s report described Dowd as “mildly obese” but otherwise healthy and with no other medical conditions.

The autopsy was performed Feb. 7 but not completed and signed off on until Thursday. Previously, Santa Clara County officials believed the first virus-related death in the county occurred on March 9, and federal officials believed the first U.S. death occurred Feb. 26 in Washington state.

UCSF pathologist Dr. Andrew Connolly, who also reviewed the report but was not involved in the autopsy, said it’s possible the virus caused the inflammation of the heart, or an autoimmune reaction did so. He also noted she had mild pneumonia.

The Santa Clara medical examiner’s office saved tissue from Dowd, as well as from two other people autopsied in February and early March, because officials saw evidence of viral infection and the victims tested negative for likely culprits including influenza. The chief medical examiner-coroner has said she suspected their deaths were because of COVID-19 but could not test them at the time.

The office sent tissue samples from the three autopsies to the Centers for Disease Control and Prevention. On Tuesday, the county received results that the three deaths, on Feb. 6, Feb. 17 and March 6, were indeed linked to COVID-19. Their infections, which were not linked to travel, indicate that the virus was spreading from person to person in the Bay Area much earlier than previously thought.

The 5-foot-1, 165-pound Dowd tested negative for the flu, parainfluenza and other respiratory illnesses, the report found. No drugs or alcohol were found in her system.

Attempts to reach Dowd’s family on Saturday were unsuccessful.

Though the coronavirus is generally known to cause respiratory illness, it can also affect other organs including the heart, intestinal tract, kidneys and brain. Patients with severe infection have been known to die from heart attacks and strokes. It’s not clear yet whether the virus itself damages organs, or whether an overactive immune response or some other factor is to blame.

A second autopsy report obtained by The Chronicle was for a 69-year-old man who died Feb. 17. The cause of death for the 69-year-old, the report says, was COVID-19 infection complicating Type 2 diabetes and hypertension.

The man also tested negative for the flu during the initial autopsy. Testing by the CDC found evidence of the coronavirus in tracheal tissue but no other major organs. No other viral infections were identified. He had reported a fever and cough before he died.

In addition to Type 2 diabetes and high blood pressure, he had heart disease, the report found. He was identified by fingerprints.

Melinek suspected that the man had tracheitis, or an inflammation of the trachea, caused by the virus. The state of the body suggests he died days earlier, she said.

“We know he had the virus, but we don’t know if it caused his death,” said Connolly of UCSF. “Did COVID cause his death? It might have.”

Other early Santa Clara cases may surface. On Friday, Santa Clara County Chief Medical Examiner Michelle Jorden wrote to the county board of supervisors that her office has retroactively tested tissue from 29 people who had flu-like symptoms when they died and found that nine tested positive for the coronavirus. The earliest of these was Dowd. Some cases are not closed, she said, and have not been included in the county’s death count which stands at 99.

Matthias Gafni and Jill Tucker are San Francisco Chronicle staff writers. Email: matthias.gafni@sfchronicle.com jtucker@sfchronicle.com Twitter: @mgafni, @jilltucker