MONDAY, Nov. 18, 2013 (HealthDay News) -- A new online cholesterol risk calculator produced by two leading U.S. heart organizations is flawed and overstates a person's risk of heart disease, a pair of Harvard Medical School professors say.

The professors contend that this flaw could lead the calculator to mistakenly suggest that millions of people should be taking cholesterol-lowering statin drugs, The New York Times reported Monday.

Key officials with the American Heart Association (AHA) and the American College of Cardiology (ACC) stood by the calculator during a hastily gathered news conference Monday morning at the heart association's annual meeting in Dallas.

Harvard professors Dr. Paul Ridker and Dr. Nancy Cook reportedly pointed out problems with the calculator a year ago, saying that it did not seem to work accurately when they tested it using patient data, the Times reported.

When the online calculator went live last week, Ridker and Cook again tested it and reported serious flaws that could overestimate a person's risk of heart disease by 75 percent to 150 percent, the newspaper reported. Their findings are to be published Tuesday in the medical journal The Lancet, according to the Times' report.

AHA and ACC officials said Monday that the Harvard professors' analysis of the calculator relied on patient data from three heart studies involving people both younger and healthier than the average American.

"These people exist in the U.S. population, but it's a very healthy, skewed group," said Dr. Donald Lloyd-Jones, chair of the department of preventive medicine at Northwestern University's Feinberg School of Medicine.

Lloyd-Jones said he and others met with Ridker on Saturday, as the AHA meeting got under way, and reviewed a limited amount of the Harvard doctors' data. He said he's still waiting to see the full report.

"I think all of us would like to see Dr. Ridker's data, and see that play out in scientific discussion rather than in the media," Lloyd-Jones said.

The two heart health groups said they created the calculator -- as well as a set of aggressive new cholesterol-lowering guidelines -- using a broad range of patient data that allowed them to incorporate factors that hadn't been included in previous risk assessments. For example, prior attempts did not include calculations for African-American populations, and did not attempt to include stroke risk.