WASHINGTON — Those lords-a-leaping and ladies dancing may want to consider the downside of the holidays: Heart attack season has arrived. December and January are the deadliest months for heart disease, and many of the things that make the season merry are culprits: Rich meals, more alcohol -- and all that extra stress.

But what may make the Christmas coronary more deadly than the same-size heart attack in, say, August, is a double dose of denial. It's not uncommon for people to initially shrug off chest pain as indigestion. Research suggests they're even more reluctant for a run to the emergency room when it means disrupting a holiday gathering, or if they've traveled to a strange city -- meaning they arrive sicker.

Minutes matter.

"You have only a short window of opportunity to save heart muscle," warns Dr. William Suddath of Washington Hospital Center in the nation's capital -- where a cardiac team on-duty 24 hours a day aims to start clearing victims' clogged arteries within 15 minutes of their arrival in the emergency room.

How bad each year is varies widely, but some hospitals say they saw an upswing in heart attacks start on Thanksgiving weekend. At Suddath's hospital, it started with a surprise spike the weekend before Thanksgiving -- with so many critically ill patients that doctors ran out of a key heart-pumping machine and had to rent two extras.

Doctors have long braced for the seasonal upswing. A 2004 study confirmed it was a nationwide phenomenon, with peaks in death coinciding around the Christmas and New Year's holidays.

Why is harder to pin down. Vanderbilt University cardiologist Dr. Keith Churchwell says a "hurricane of factors" can tip someone at risk of a heart attack over the edge during this busy time of year.

"You can't be too busy to ignore your cardiovascular health," he says -- but that's a key excuse he hears from his own patients.

Consider:

• Busy revelers tend to skip their medications, forget them when traveling or be unable to get refills far from home.
• What dieter can resist holiday goodies? The few extra pounds so many people gain will haunt you long-term. Right away, a particularly heavy meal, especially a high-fat one, stresses the heart as it is digested. Blood pressure and heart rate increase. There's even evidence that the lining of arteries becomes temporarily more clot-prone.
• Too much salt has an even more immediate effect, causing fluid retention that in turn makes the heart have to pump harder.
• Alcohol in moderation is considered heart-healthy. But if a round of holiday parties leaves you tipsy, that, too, makes your heart pump harder to get blood to peripheral arteries.
• Worse is something called "holiday heart syndrome," where alcohol literally irritates the heart muscle to trigger an irregular heartbeat called atrial fibrillation. If a-fib goes unchecked for too long, it in turn can cause a stroke.
• People say they're too busy to exercise, especially as it gets cold and darkness falls earlier. It can take months to build back up to pre-holiday exercise habits.

As for cold weather, it can constrict blood vessels, and the extra exertion of snow shoveling can cause a heart attack. The usual winter rise in respiratory diseases is another risk, adding further burden to a stressed heart -- another reason to get a flu shot.

But the holiday spike happens even in warm climates.

And delay in treatment plays a role.

Hospitals may be short-staffed during the holidays, slowing the time it takes to diagnose a heart attack and start clearing the blocked artery, says Dr. Alice Jacobs of Boston University, past president of the American Heart Association.

The good news: The nation's hospitals are undergoing a major shift to speed care to heart attack sufferers. It's called "door to balloon time," and the aim is to reopen blocked arteries with angioplasties or other procedures within 90 minutes of arrival.

Only about a third of people suffering major heart attacks get such fast care now. But more than 900 hospitals have signed on to meet that challenge -- sites that either are forming 24-hour cardiac catheterization teams like Suddath's, or making sure on-call doctors arrive within minutes, or ferrying patients to those angioplasty centers.

But for the hospital overhaul to work, patients can't hesitate when symptoms strike.

"If you have symptoms, don't ignore them, wherever you are," Jacobs stresses.

Yet realizing you're having a heart attack can be hard. Terry Bieber was just 50 when she woke up two days after Thanksgiving 2006 feeling what she thought was indigestion, got some Tums and returned to bed. Sometime later her husband realized she was sweating heavily while her skin was cold to the touch. Still, she argued when he went to call 911.

Like many women, Bieber didn't feel classic chest pain or pain radiating down her arm. She had to be helicoptered from the hospital near her Prince Frederick, Md., home to Washington Hospital Center for emergency angioplasty of two arteries.

"Don't take any chances," she now advises. "I had no clue at all that's what it was. ... If I had been by myself, I probably would not have called 911."