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For years, cardiologists were aware that heart attacks are more common during the winter months than in any other season. Most assumed that the cause was cold weather. But then researchers in California examined death certificates in Los Angeles County, an area not known for its inclement winters, and found that, even there, fatal heart attacks spiked during the winter months. More specifically, they started rising around Thanksgiving, climbed inexorably through Christmas and peaked on New Year’s Day. A subsequent study of death certificates nationwide, published in Circulation in 2004, confirmed the association between the two holidays and heart-attack deaths. It was accompanied by a cheery editorial headlined “The ‘Merry Christmas Coronary’ and ‘Happy New Year Heart Attack’ Phenomenon.”

Why the number of heart-attack deaths should surge so significantly during the holidays still is not clear, although cardiologists have some well-founded guesses. “We suspect there is often an inappropriate delay in seeking medical attention” at this time of year, says Dr. Robert A. Kloner, a professor of medicine at the University of Southern California, a cardiologist at Good Samaritan Hospital and the lead author of both the 2004 study of deaths in Los Angeles County and the accompanying editorial. “People ignore the pain in their chest,” perhaps because they don’t wish to disrupt the festivities or they misinterpret the ache as overindulgence, Dr. Kloner says. By the time they get to an emergency room, it’s too late to save them. Stress and tension likely play a role, too. “Spending time with family members can be trying,” he says. “And there are often concerns about financial issues, buying presents and so on.” Even a wood-burning fireplace, a romantic symbol of wintry, holiday evenings, could be a contributing factor, because particulate matter in the air has been connected to an increase in the risk of heart attacks, Dr. Kloner says.

A provocative new study published this year in the journal Heart and Circulatory Physiology suggests, however, that there may be a novel way to test at least one element of your heart’s health right in your own living room, right in the middle of the holidays. Sit on the floor with your legs stretched straight out in front of you, toes pointing up. Reach forward from the hips. Are you flexible enough to touch your toes? If so, then your cardiac arteries probably are also flexible.

In the study’s experiment, scientists from the University of North Texas and several Japanese universities recruited 526 healthy adults between the ages of 20 and 83 and had them perform the basic sit-and-reach test described above, although their extensions were measured precisely with digital devices. Taking into account age and gender, researchers then sorted the subjects into either the high-flexibility group or the poor-flexibility group.

Next, using blood-pressure cuffs at each person’s ankles and arms, researchers estimated how flexible their arteries were. Cardiac artery flexibility is one of the less familiar elements of heart health. Supple arterial walls allow the blood to move freely through the body. Stiff arteries require the heart to work much harder to force blood through the unyielding vessels and over time could, according to Kenta Yamamoto, a researcher at North Texas and lead author of the study, contribute to a greater risk for heart attack and stroke.

What the researchers found was a clear correlation between inflexible bodies and inflexible arteries in subjects older than 40. Adults with poor results on the sit-and-reach test also tended to have relatively high readings of arterial stiffness. In short, the study concluded that “a less flexible body indicates arterial stiffening, especially in middle-aged and older adults.” No such correlation was found in those under 40, even when gender and fitness were considered as factors.

These results do not mean, of course, that people in the inflexible group were in imminent danger of a heart attack on Christmas Day. Arterial stiffening does not indicate or inevitably lead to arterial disease, Mr. Yamamoto emphasizes. In fact, some degree of arterial stiffening is inevitable with age. But the stiffer your arteries are, the less efficient your heart.

How it is that stiff muscles in the back and legs are linked to stiff tissues near the heart is an issue that hasn’t been fully elucidated, Mr. Yamamoto says, although arterial walls are composed of the same kinds of elastic tissues as muscles elsewhere in the body. So it’s likely, he says, that alterations in the composition of muscle tissues in the lower back (including aging-related alterations in the amount of collagen within the muscles) could be occurring in the arterial walls at the same time.

What is surprising are some early indications that increasing your flexibility might somehow loosen up your arteries, too. That was the accidental and, as yet unreplicated finding of a small 2008 study at the University of Texas at Austin. The study was designed to examine whether weight lifting increased arterial stiffness. (It didn’t, at least on this occasion.) The control group consisted of people who stretched. They were not expected to show any change in cardiac function, but over the course of 13 weeks they in fact increased the pliability of their arteries by more than 20 percent.

Mr. Yamamoto and his colleagues are currently conducting an ambitious study to determine just how and whether stretching directly affects the arteries. The results won’t be available for some time. Until then, Mr. Yamamoto says, it’s best to consider your flexibility (or lack thereof) as a marker of your probable arterial elasticity. “If you can touch your toes in the sit-and-reach test, your flexibility is good,” he says. If you can’t, you might consider talking to your cardiologist — although, remember, as Mr. Yamamoto points out, that tight arteries are not necessarily diseased arteries. They’re just less than ideally fit.

As for avoiding the “Merry Christmas Coronary,” Dr. Kloner’s advice is succinct: “Don’t ignore symptoms,” he says. Avoid overimbibing, too, and tamp down stress. If this requires turning down an invitation from a wheedling relative, you could always try explaining that your cardiologist would say that it’s for the best.