The document, obtained by ET, reveals that the Brady Bunch star had been suffering from coronary artery disease for 10 years and atrial fibrillation -- also referred to as an irregular heartbeat -- for the past five years.
Henderson, who died on Nov. 24, surrounded by her four children, recorded a video earlier this year for Go Red for Women -- the American Heart Association's campaign to raise awareness about heart disease and strokes among women.
In the clip, the star opened up about her own ongoing battle with heart health.
"I knew as a child that I had a heart murmur," Henderson shared in the clip. "And as I got older, I was experiencing more irregular heartbeats. So finally, I went to a cardiologist about eight years ago and I was in really bad shape."
Henderson recounted how she ended up in the emergency room at Cedars-Sinai in Los Angeles, where she underwent heart surgery to fix her damaged mitral valve.
"I urge women to have your heart checked. Go to a cardiologist," the actress shared in the video. "If I can help one person and save one person's life, then I'm thrilled."
See more on the veteran star's celebrated life and legacy in the video below.