Australian researchers used data from the National Mortality and Air Pollution Study, which looked at health and weather pollution in the United States from 1987 to 2000 during which 4 million heart attacks or strokes occurred.

The researchers plotted daily deaths against fluctuations in temperature during one day, they found that ozone was a common link.

The study, published in Occupational and Environmental Medicine, found a 10 degree temperature increase on the same day was associated with a rise in heart disease or stroke deaths of just over 1 percent at the lowest ozone level and by more than 8 percent for the highest levels.

Ozone is chemical pollutant generated by a reaction between nitrogen oxides, volatile organic compounds and oxygen in the presence of sunlight.