Scientists in Britain say a dose of winter infections such flu can double the risk of heart attacks and strokes.
An extensive study by scientists from the London School of Hygiene & Tropical Medicine's Medical Statistics Unit has revealed that the risk did not depend on age or gender and victims are twice as likely to be affected in the week after catching a respiratory infection.
For the comprehensive study the scientists examined two million patients registered with approximately 500 GPs and found the increased risks associated with flu were a 'substantial public health problem' that kills thousands of people every year.
The research has prompted renewed calls from experts and campaigners for all those with heart disease to have the flu jab in order to minimise their risk.
The GP database was used to identify all cases of a first-time diagnosis of MI or stroke and it was found of the 300,000 people who suffer heart attacks in Britain each year, 117,000 of them are fatal and more than 130,000 people in England and Wales suffer a stroke each year.
The scientists believe that infections such as flu dislodges fatty deposits that build up in the arteries, leaving them free to move around the body and clog up the brain or heart where they block the blood flow.
Around 23,000 more people die in winter than in summer and of the two million people whose GP records were studied, 11,000 had suffered a heart attack and were twice as likely to have been diagnosed with flu or a respiratory infection in the previous month.
The 9,000 who had suffered a stroke were twice as likely to have been diagnosed with a respiratory infection in the past three days.