An estimated 400,000 women die every year of heart disease, 10 times more than die of breast cancer annually, according to the American Heart Association.
Symptoms can include pressure, a tightening or heaviness, not necessarily pain. Flu-like symptoms, nausea, shortness of breath and excessive fatigue are also common.
Some women just stay at home because it is not painful enough to seek help. Others even say their earlobes hurt, McNicholas said. And the risk increases as women reach menopause, "catching up" with men's risk.
McNicholas was in her "prime" when she had a heart attack at 54, working 100 hours a week as a surgeon and going to law school at night. "I had every reason to feel fatigued," she said.
"My back and shoulders ached," she said. "I looked gray, but we don't ask other people how we look or say how terrible we feel. We lay on the couch and figure it's going to pass.
"The point is we don't want to go to the emergency room and make a fool out of ourselves if we don't have a good story."
She didn't seek help for a month, but came to her senses while on holiday at the Jersey Shore when her sister reminded her that both her parents had died of heart disease.
"My sister slept on the same floor as me, and the next morning she said, 'You coughed all night. ... Mom coughed like that when she died.' ... That's what pushed me. You have to have someone else notice."
McNicholas began a program at Christiana Care called "No Heart Left Behind," encouraging teens to educate their middle-aged mothers about heart disease.
One of her students saved her mother-in-law's life on a ski vacation, insisting she go to the emergency room, even when everyone else around her said it was altitude sickness. The woman was perfectly fit, walking five miles a day.
As for O'Donnell, McNicholas said the comedian likely "sure looked like hell and should have said to her partner, 'How do I look?' and gone to the hospital."
O'Donnell is recovering. She is "resting at home and doing fine," according to her publicist. She also tweeted her support for the American Heart Association campaign "Go Red for Women": "Sign me up," she wrote. "Let's get the word out there -- count me in."
"I am lucky to be here," O'Donnell wrote on her blog. "Know the symptoms ladies, listen to the voice inside. The one we all so easily ignore. CALL 911."