Nicholas Brendon’s cause of death has been revealed.

The “Buffy the Vampire Slayer” star, who died on March 20 in Indiana, died of atherosclerotic and hypertensive cardiovascular disease with acute pneumonia and previous myocardial infarction (heart attack) being contributing factors, according to his autopsy results obtained by Page Six.

Arteriosclerosis occurs when the blood vessels that carry oxygen and nutrients from the heart to the rest of the body — the arteries — become thick and stiff, hardening over time.

Meanwhile, acute pneumonia is an intense, sudden-onset infection that causes inflammation in one or both lungs, filling the air sacs with fluid or pus.

The manner of death was natural, and the mechanism of his death was 90% blockage of his right coronary artery.

Putnam County Coroner Todd Zeiner explained in his autopsy report, “Autopsy demonstrated an adult male with a markedly enlarged heart, severe stenosis of the right coronary artery, moderate stenosis of the left anterior descending and left circumflex arteries, acute pneumonia and inflammation of the small bowel. The small bowel inflammation is most likely secondary to ischemic changes related to the cardiogenic shock.”

Brendon’s longtime manager and friend, Theresa Fortier, was the person who found him on his couch and called 911.

“There was no resuscitation attempt made due to obvious signs of death,” Zeiner explained in his autopsy report. “I presumed time of death was around 6 a.m. due to body temp and rigor/livor [mortis] signs.”

Zeiner added, “He was markedly coughing and had a ‘raspy’ voice. Theresa stated the decedent had been having a persistent cough and had been self medicating with over the counter medications. He had been complaining about chest pain.”

Fortier reportedly recommended that Brendon go to the hospital, but he declined.

“He was a longtime smoker and was apprehensive about going due to his recent back surgery,” Zeiner wrote.

Brendon’s family previously announced that he had “passed in his sleep of natural causes” at the age of 54, noting that “most people know Nicky for his work as an actor and for the characters he brought to life over the years.”

They continued, “In recent years, Nicky [had] found his passion in painting and art. Nicky loved to share his enthusiastic talent with his family, friends and fans.”

Brendon was “passionate, sensitive and endlessly driven to create,” his family insisted. “Those who truly knew him understood that his art was one of the purest reflections of who he was.”

They went on, “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 family concluded by asking for “privacy” to “grieve his loss and celebrate the life of a man who lived with intensity, imagination and heart.” They also thanked those who have “shown love and support.”

Zeiner previously told Page Six that Brendon “resided alone and was discovered by a longtime friend who had been staying overnight to provide care.”

Zeiner said the pal — whose identity is unknown — found Brendon “positioned as if asleep,” and he was pronounced dead by medical personnel with “no signs of foul play … and nothing at the scene indicat[ing] the death was anything other than natural.”

Throughout his life, Brendon — who went to rehab several times for alcoholism and drug addiction — had various run-ins with the law, including in 2021 when he was arrested and charged with prescription fraud and refusal to identify himself to police.

After pleading guilty to the felony, the misdemeanor charge was dismissed, and Brendon was sentenced to a year of probation.

The “Criminal Minds” actor — who had also been accused of domestic violence and sexual misconduct — was facing unrelated legal challenges as well as health issues at the time of his death.

He was diagnosed with cauda equina syndrome (CES) after a serious fall in 2021, which required multiple spinal surgeries and led to partial paralysis in his legs and genitals.

He later experienced two cardiac incidents, including a heart attack, that led to the discovery of a congenital heart defect.

Brendon addressed his difficulties in a 2023 Instagram post, lamenting in part at the time, “I’ve had multiple doctor appointments to juggle, and dealing with health insurance and pre-approvals feels nearly as emotionally exhausting and painful as dealing with my actual injuries.”

Many of Brendon’s “Buffy” co-stars posted Instagram tributes after his passing, including Sarah Michelle Gellar, who played Buffy Summers in the popular drama series.

The actress uploaded a throwback photo of the pair and quoted Brendon’s character, Xander Harris, in the caption, writing, “‘They’ll never know how tough it is to be the one who isn’t chosen. To live so near to the spotlight, and never step in it. But I know. I see more than anybody realizes, because nobody’s watching me.'”

She added, “I saw you Nicky. I know you are at peace, in that big rocking chair in the sky.”