Over the last 30 to 40 years, children born with heart defects have been living longer, which means the population of adults with congenital heart defects has gotten larger, said Dr. Suzanne M. Gilboa from Centers for Disease Control and Prevention in Atlanta, Georgia.

But the fact that the adult population is approximately 40 percent larger than the child population - 1.4 million vs 1 million - "was somewhat surprising," she told Reuters Health by email.

Back in 2000, two research teams estimated that fewer than 1 million Americans were living with these heart defects.

The U.S. has no way of tracking congenital heart defect statistics, so Gilboa's team joined forces with Canadian colleagues and used the Québec Congenital Heart Disease Database to estimate the rates of these conditions in the U.S. in 2010.

They assumed rates in Québec would be similar to that among whites in the U.S., and they adjusted their calculations to estimate rates for non-Hispanic black and Hispanic populations.

Using these methods, they determined that approximately 2.4 million people were living with congenital heart defects in the U.S. in 2010. One of every eight of these individuals (about 290,000) had severe heart defects.

The rate was higher in children (13 per 1000 children) than in adults (six per 1000 adults), but there were more adults (approximately 1.4 million) than children (approximately 1 million) living with congenital heart defects.

Estimated rates were higher in whites and Hispanics than in blacks, and slightly higher in females than males, according to a report in the journal Circulation.

"Compared with population estimates generated for the year 2000, the current estimates for the year 2010 represent a 40 percent increase in the total number of individuals living with congenital heart defects in the U.S. and over a 60 percent increase in the size of the adult population alone," the researchers note.

Gilboa said the key message is that people with congenital heart disease need "appropriate care across the lifespan, not just during childhood."