The 50-year-old former daytime host credited her survival to quick Internet research on her painful symptoms and an aspirin she had seen recommended in TV commercials.
"Thank god, saved by a tv commercial, literally," she wrote in her usual verse form on her rosie.com blog, which uses a heart on the Web page instead of a dot to separate "rosie" from "com."
She ended up having a mesh tube called a stent inserted into one of her heart's arteries after doctors discovered it was 99 percent blocked.
She explained she was in a parking lot in her Hudson Valley hometown of Nyack, N.Y., when she "heard a loud commanding voice" asking for help and "saw an enormous woman struggling to get out of her car."
O'Donnell helped the woman out of her car. "It was not easy but together we did it," she wrote. The woman "was up and on her way with gratitude."
"A few hours later my body hurt," O'Donnell wrote. "I had an ache in my chest, both my arms were sore, everything felt bruised."
She first thought it was "muscular" or a "pulled tissue" after straining to help the woman.
But the pain persisted, she felt nauseated, "my skin was clammy, i was very very hot, i threw up."
It couldn't be a heart attack, she said she thought. But she "googled women's heart attack symptoms" and discovered she had "many of them."
She took some aspirin, but didn't call emergency paramedics, choosing instead to visit a cardiologist the next day.
An electrocardiogram, or EKG, revealed the massive blockage in her left anterior descending artery -- a condition she said doctors colorfully refer to as a "widow maker" -- because if the artery gets abruptly and completely blocked it will cause a massive heart attack that will likely lead to a sudden death.
"I am lucky to be here," O'Donnell wrote.
"Know the symptoms ladies, listen to the voice inside. The one we all so easily ignore. CALL 911. save urself xxx," she concluded after citing statistics that 50 percent of U.S. women suffering heart attacks don't call the emergency telephone number.
"She is now home and resting comfortably. She is very, very lucky," an O'Donnell spokesman told People magazine.
Early this month, O'Donnell said her fiancee, Michelle Rounds, was diagnosed with desmoid tumors, a very rare affliction that can destroy tissue like a cancerous tumor.