It’s the most wonderful time of the year. It’s also a time when heart attacks and strokes spike.

Research shows heart attacks spike by 30% to 40% in the last two weeks of the year.

Dr. Donald Lloyd-Jones, chair of preventive medicine at Northwestern University’s Feinberg School of Medicine and a Northwestern Medicine cardiologist, says a combination of factors like cold weather and the stress of the holiday season can contribute to the spike.

“When we breathe colder air, it cools the blood as it passes through our lungs and when that cold blood hits the coronary arteries that feed the heart muscle, the coronary arteries tend to constrict or get smaller,” said Lloyd-Jones.

If there is an already compromised blood flow to the heart, activities in the cold weather, like shoveling snow, create the perfect storm for a heart attack to happen, he said.

Heart attack and stroke remain the leading causes of death in the U.S. Lloyd-Jones says any sudden onset of symptoms should be taken seriously.

In men, sudden heavy, crushing chest pressure in the middle of the chest or sudden, unexplained shortness of breath are signs of a possible heart attack.

Women can have the same symptoms but can have other subtle symptoms like occasional dizziness and lightheadedness or profound fatigue.