Transplanted hearts do not survive as long in black children as they do in other ethnic groups, a study says.
Researchers analysed thousands of child patients
Researchers from Emory University in Atlanta found hearts survived for less than half the time in black children than they did in others.
The Journal of Pediatrics report said the cause of the findings was unclear and further research was needed.
UK heart experts said knowing more about the issue could lead to tailored treatment.
The team analysed records of 4,227 child heart transplants. In 17%, the recipients were black children.
The researchers found that 51% of black recipients survived for five years, compared with more than two-thirds of children from other ethnic groups.
The transplanted heart lasted 11 years in children from other groups, while those given to black youngsters survived just 5.3 years.
Lead researcher William Mahle said social-economic status had been taken into account, but the findings could not be explained by differences in health insurance or background.
"We can't just chalk it all up to having lower income.
"African-Americans on average have lower incomes, but it doesn't look like that's the issue.
"We are starting to understand there are biological differences between groups and that maybe we'll need to tailor medications or our approach to transplant a bit differently."
But while he said the issue was still not fully understood, there were still some immediate implications.
"We need to be honest with families when we counsel them about a transplant in a child who is African-American and tell them that they cannot honestly expect the same survival of that heart as a white or Asian child."
He said families might also want to consider options other than transplantation.
Robert Gaston, a transplant expert at the University of Alabama, said differences between ethnic groups in transplants had been first noticed in the 1970s, but this study confirmed that the differences seen in adults could also be applied to children for heart transplants.
And he added: "As the transplant community has responded with vigour and creativity to other problems that have emerged over the last half century, we must also apply these same attributes to better understand, and ultimately rectify, ethnic disparities in solid organ transplantation."
John Dark, professor of cardiothoracic surgery at the Freeman Hospital in Newcastle, said the US, where there were many different ethnic groups, had more problems with tissue-matching than western Europe with its more stable population.
But he said the prospect of tailored medicine while at an early stage was exciting as it could alleviate some of the problems.
British Heart Foundation medical director Professor Peter Weissberg agreed further research was important. "There is emerging evidence that some ethnic groups may respond differently to certain drugs. Further research is required to define precisely why African-American children appear to do less well after heart transplantation than other children."