However, white people who carry the same genetic mutation do not appear to be at any increased risk.
The gene in the study controls production of a protein - thrombomodulin - which is found in the lining of the blood vessel walls.
The protein converts the enzyme thrombin from a clotting agent into an anti-clotting agent.
A team from the Houston Health Science Center at the University of Texas examined a tiny mutation in the gene that renders thrombomodulin useless.
A lack of effective thrombomodulin is linked to blood vessel damage, blood clots and heart disease.
Reduced levels of normal thrombomodulin as a result of the altered gene may cause an increased tendency for blood vessel damage and blood clots.
Lead researcher Dr Kenneth Wu said: "We have identified a genetic marker for predicting increased heart attack risk in African-Americans.
"Our findings underscore the importance of studying genetic risk factors by ethnic group."
The researchers analysed data from a major study of heart disease across different communities.
Each person has two copies of the thrombomodulin gene - one from each parent.
After taking account of other risk factors, they found that black people with at least one mutated form of the gene were 6.1 times more likely to suffer coronary heart disease.
Reason unclear
Why the gene mutation should affect black people, but not whites is not clear.
Dr Wu believes it is possible that the gene may act differently in blacks than in whites.
He said: "There is no good information of any kind regarding different expression or function of a gene product among ethnic groups.
"However, it is possible that environmental factors may influence the way the gene works."
Dr Wu said more research was needed to confirm the findings.
A spokesman for the British Heart Foundation said: "There is evidence that some people are genetically at a greater risk of developing coronary heart disease.
"As the researchers themselves acknowledge this is a small sample of American Africans. Further research such as this is required to improve our understanding of genetic differences between ethnic groups in relation to coronary heart disease."
The research is published in Circulation: Journal of the American Heart Association.