The researchers examined how the incidence of MI in Sweden had changed with the summer and winter clock shifts since 1987.
Overall, they found that the number of heart attacks increased by 5 per cent during the first week of summertime.
The risk was greatest in the first three days after the clocks went forward, and for people under the age of 65.
But readjusting the clocks back to winter time reduced the risk of suffering a heart attack in the following week.
Lead researcher Dr Imre Janszky, from the Karolinska Institute in Stockholm, said that the disruption in the chronobiological rhythms, the loss of one hour's sleep and the resulting sleep disturbance were the probable causes for the increased MI risk.
The researchers add that they hope the research findings will lead to an improved understanding of how night and day cycles can have an impact on patients' health.
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