LOS ANGELES — There’s a new forecast of the cost to treat heart disease in the U.S. over the next 20 years — and it isn’t pretty.

According to a study published Monday in Circulation: Journal of the American Heart Association, the annual cost to treat heart disease — including high blood pressure, coronary heart disease, heart failure, stroke and other conditions — will triple by 2030, from $273 billion to $818 billion.

U.S. medical expenditures are already the highest in the world, hitting 15 percent of gross domestic product in 2008, the authors reported.

To generate the forecast, researchers took current disease rates and applied them to population estimates suggested by census data. They assumed no major changes in treatment.

Today, 36.9 percent of Americans have some form of heart disease. By 2030, 40.5 percent will, according to the Circulation study. Cases of both stroke and heart failure were projected to rise about 25 percent.

The most expensive condition to treat will remain hypertension, because of its prevalence. Hypertension is a risk factor for stroke, coronary heart disease and heart failure.

Shortages of doctors or nurses could push costs even higher, the study authors wrote. Continued rises in rates of diabetes and obesity could too, they said. The researchers estimated that more than half of the increase in hypertension cases would be caused, at least in part, by Americans’ increasing body mass. The ill effects of the obesity epidemic are poised, they wrote, to reverse the progress made when many Americans quit smoking.