The flu is dangerous for everyone, but researchers say people with heart disease are especially at risk.
"The frequency of heart attacks and threatened heart attacks completely coincides with the flu season," said Dr. Lawrence O'Connor, an interventional cardiologist at Glendale Memorial Hospital.
He says the inflammation that accompanies the flu can loosen plaque in your arteries and increase the risk for clots.
"Our immune system goes on red alert, wipes out the viruses and looks around for something else to do and finds a plaque sitting in an artery and decides to go after that," said Dr. O'Connor.
A recent report in the Canadian Medical Association Journal found middle-aged and older adults who get the flu vaccine may be less likely to suffer a first-time heart attack in the following year than those who skip the shot.
A flu vaccine is already recommended for adults age 65 and older, as well as those with heart disease and certain other chronic medical conditions.
During flu season, Dr. O'Connor also tells his heart patients to wash their hands often, avoid big crowds and take their daily aspirin.