'Buffy' Star Nicholas Brendon Cause of Death Revealed

"Buffy the Vampire Slayer" star Nicholas Brendon died from complications related to cardiovascular disease ... and his death has been ruled natural, TMZ has learned.

The actor was found deceased on a couch inside a Putnam County, Indiana residence on March 20, according to a report from the Putnam County Coroner obtained by TMZ. He died from atherosclerotic and hypertensive cardiovascular disease, which is caused by plaque buildup in arterial walls, per the American Heart Association. Specifically, he had a 90% blockage of the right coronary artery. Page Six was first to report on his cause of death.

He also had acute pneumonia and previously had a heart attack, which are listed as contributing factors in his death. His friend had been staying with him to take care of him as his health declined, and the friend told the coroner he had a heart attack "several years ago" but declined any further treatment at that time.

Brendon's pal said she had last seen him around 5 AM the morning he passed and heard him coughing. She found him unresponsive around 8 AM and immediately called police. She also said he had been complaining about chest pain but declined a hospital visit and was self-medicating with over-the-counter medications.

Brendon was a longtime smoker and was "apprehensive about going due to his recent back surgery," according to the report.

The coroner stated surveillance video of the home showed he was "markedly coughing" and had a "raspy" voice leading up to his death.

Brendon was a series regular on 'Buffy' opposite Sarah Michelle Gellar, portraying Xander Harris during the series' 7 seasons.

After his death, his family said he had recently "found his passion in painting and art."

They added ... "While it’s no secret that Nicholas had struggles in the past, he was on medications and treatment to manage his diagnosis and he was optimistic about the future at the time of his passing."

The actor's family members also revealed a history of cardiac issues ... he suffered a heart attack in 2023 and was later diagnosed with a congenital heart defect

We told you previously Brendon was charged with domestic violence in 2017 after attacking his girlfriend while under the influence of alcohol.