Among 332 heart attack patients, the complication was six times more likely to strike following a bout of the flu, researchers reported.
The Canadian team looked at almost 20,000 cases of laboratory-confirmed flu infection from 2009 to 2014.
The study was based on almost 20,000 adult cases of laboratory-confirmed influenza infection in Ontario, Canada from 2009 to 2014.
About one-third of the patients with influenza-associated heart attacks died.
Lead scientist Dr Jeff Kwong, from the Institute for Clinical Evaluative Sciences (Ices) in Ontario, said: "Our findings, combined with previous evidence that influenza vaccination reduces cardiovascular events and mortality, support global guidelines that advocate for influenza immunisation in those at high risk of a heart attack".
A bad case of the flu can cause a sixfold increase in the risk of a patient having a heart attack within a week, according to a study involving 20,000 people with laboratory-confirmed influenza.
"This season in particular has been devastating for patients with heart disease, diabetes, asthma because when they get the flu, their risk for having respiratory problems including death have been very high".
"If you have heart disease, you take it as gospel that you should do things like take your cholesterol medication and keep your blood pressure under control", said lead researcher Dr. Jeffrey Kwong.
Philippa Hobson, from the British Heart Foundation, said: "There is evidence that heart attacks happen more often during or immediately after an acute inflammatory illness, such as flu".
As well, viral infections cause inflammation, which promotes blood clots forming in the blood vessels that serve the heart, again leading to a heart attack.
Going to your doctor for a flu shot may protect you from more than just a fever and the sniffles.
And for years, the American College of Cardiology (ACC) and other groups have recommended that people with heart disease get an annual flu shot. There was one strong pattern: 20 had a heart attack within a week of getting the flu.
"This time of year we frequently had people on the floor after the flu", she told Reuters Health by phone.
Dr. Erica Jones, director of the HeartHealth Program at Weill Cornell Medicine and New York-Presbyterian Hospital, who was not connected with the study, said the results aren't surprising based on her experience with hospitalized heart attack patients.
Still, other measures - like regular hand washing - are important, too. "Even if the flu shot isn't ideal, it may protect at least somewhat and the flu could be less severe, although this study didn't address that".
The American Heart Association has more on flu and pneumonia prevention.
The full study was published January 25 in the New England Journal of Medicine.
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