Not to dampen any holiday spirits, but studies show heart troubles rise this time of year.

It's not just a Western phenomenon. Recent research in China found the same thing. The increase includes fatal and nonfatal heart attacks and a less serious condition dubbed "holiday heart syndrome" — an irregular heartbeat caused by too much alcohol.

Reasons for the seasonal increase are uncertain. Theories include cold weather, overindulgence and stress.

"The other day we had three heart attacks come in within four hours," said Dr. Charles Davidson, chief of Northwestern Memorial Hospital's cardiac catheterization services. The hospital's usual rate is two or three a week.

American Heart Association spokesman Dr. Richard Stein, a cardiologist at New York University's medical center, said most studies investigating holiday heart trends have found a statistical increase in heart attacks and other problems — not a giant surge but worth noting just the same.

It happens in cold climates, sometimes when sedentary people or those with heart disease take on too much snow shoveling, or spend too much time outdoors. Cold weather can constrict arteries, increasing demand on the heart, he said. But it also happens in warm places.

Flu season coincides with winter holidays, and Stein said that might be a factor since the virus can cause inflammation that can stress the heart.

Stein recommends the usual preventive advice, including flu shots, avoiding excessive eating and drinking, and getting enough exercise throughout the season.

David Phillips, a sociologist at the University of California's San Diego campus, has long studied when people die. His research, based on millions of U.S. death certificates, shows that cardiac deaths including fatal heart attacks increase almost 5 percent on Christmas Day, the day after and on New Year's Day. Deaths from other causes also increase at holiday time, but not as much, he has found.

Phillips estimates that there are 2,000 extra deaths each year, mostly from heart-related problems, linked with Christmas and New Year's. He says hospitals' holiday staffing is a factor, with fewer doctors and nurses working and the most senior employees often on vacation.

Also, he said, in the rush leading up to the holidays, people tend to ignore symptoms — which can be dangerous.

His advice? Head to the emergency room with life-threatening symptoms such as chest pain, unexplained falls, numbness or tingling. But for non-emergencies and elective surgeries, you might want to consider holding off until hospital staffing is back to normal.

Then there's "holiday heart syndrome," a type of irregular heartbeat called atrial fibrillation brought on by too much alcohol.

It involves irregular contractions in the heart's upper two chambers that patients often feel as palpitations, a funny fluttery sensation in the chest, or chest pain.

"People who come in with this, they're shocked that it happened," said Dr. Deepak Bhatt, a heart specialist at Brigham and Women's Hospital and editor-in-chief of the Harvard Heart Letter. Many aren't chronic drinkers and "may not realize that excess drinking at the annual Christmas party has its own risks," he said.

The condition typically happens in otherwise healthy adults, and resolves within 24 hours.