An increase in heat waves driven by climate change is causing hundreds more heart disease deaths in the United States each year, with men and Black people at particular risk, researchers say.

Each year, the United States now has about three times as many heat waves as in the 1960s. Heat can put increased strain on the heart and trigger heart attacks and other cardiac problems.

"These results suggest the full extent of the adverse health effects of extreme heat is broader than previously realized," said study lead author Dr. Sameed Ahmed Khatana. He is an assistant professor of medicine at the University of Pennsylvania, in Philadelphia.

"Climate change and its consequences will have a very large impact on our society in terms of health, and cardiovascular health is an important component of that," Khatana said in a news release from the American College of Cardiology.

For this study, his team analyzed temperature trends and heart-related deaths in all 3,108 U.S. counties in the 48 contiguous states. The researchers determined each county's average daily maximum temperature from 1979 to 2007, and then identified extreme heat days from 2008 through 2017.

Extreme heat days were defined as those when the heat index reached 90 degrees Fahrenheit or higher, and the maximum was in the 99th percentile for that day.

Between 2008 and 2017, each additional day of extreme heat in a month was associated with an overall 0.13% increase in deaths from heart disease. That worked out to an average of 600 to 700 extra deaths per year.

But there were significant gender and racial differences, the investigators found. Each day of extreme heat was associated with a 0.21% increase in heart disease deaths among men. There was no significant link for women.

And each day of extreme heat was associated with a 0.27% increase in heart disease deaths among Black people. No significant association for white people or Hispanic individuals was found.

These findings indicate that men and Black people are at higher risk for fatal heart events in heat waves, according to the study authors.

The study findings are scheduled for presentation April 2 at a meeting of the American College of Cardiology, which will be held online and in Washington, D.C. Research presented at meetings should be considered preliminary until published in a peer-reviewed journal.

Khatana said policy leaders need to realize that climate negotiations have a real impact on people's health.

"The health impacts of climate change have been happening for a while and are likely to continue to get worse with rising temperatures," he added.