Cause of death revealed for Clint Eastwood's longtime girlfriend Christina Sandera

Christina Sandera — the longtime girlfriend of Clint Eastwood — died of a heart attack, the Monterey County Health Department has reportedly confirmed .

Her immediate cause of death was listed as cardiac arrhythmia, a disorder in which, according to the Mayo Clinic, the electrical impulses in the heart malfunction and cause an abnormal heartbeat. Atherosclerotic coronary artery disease was listed as an additional condition leading to her death, according to a Tuesday report in the New York Post.

Eastwood announced Sandera's death in a statement last Thursday, although no cause of death was given at the time. She was 61 when she died July 18.

Sandera was on the board of directors for the Monterey Bay National Marine Sanctuary Foundation, where she served as the chief developer, and manager of a world-class equestrian center in Carmel Valley.

“Her commitment to both land and marine animals was truly inspiring,” the organization said in a statement on Instagram. Sandera and Eastwood hosted their annual Sea Stars Gala; the statement said she “eschewed the spotlight,” despite being connected to the high-profile Oscar winner.

“She was a ‘roll up your sleeves’ kind of person, always hands-on and deeply involved in her passions,” the chapter director of the foundation said.

Eastwood, 94, and Sandera dated for a decade, and kept their relationship largely private. They reportedly met at Eastwood’s Mission Ranch Hotel and Restaurant, where Sandera worked as a hostess. The two lived together in Carmel-by-the-Sea, a small coastal town on the Monterey Peninsula where the actor once served as mayor.

The animal activist accompanied the “Unforgiven” actor on multiple red carpets, including at the 2015 Academy Awards, their public debut as a couple. Eastwood directed and co-produced “American Sniper,” which was nominated for six awards that year.

“Christina was a lovely, caring woman, and I will miss her very much,” Eastwood said in his Thursday statement.

His youngest daughter, Morgan Eastwood, also posted a tribute.

“A devastating loss for our whole family,” she said on her Instagram story . “Thank you Christina for being a good partner to my Dad, you will be missed.”

This story originally appeared in Los Angeles Times .