DALLAS (CNN) -- Combining existing heart screening tests could detect hidden heart problems in certain people with high exercise tolerance, researchers said Monday.

A recent study found that the use of radioactive imaging along with a treadmill test could identify patients at risk for heart attack or who need bypass surgery or a balloon angioplasty.

Researchers had patients exercise on a traditional treadmill before injecting them with radioactive material. Doctors then used a picture or scan of the heart called a radioisotope image to see how much of the radioactive material is flowing into the heart.

A blockage would indicate the possibility of heart attack, stroke or the need for a surgical procedure to reduce such a blockage.

Researchers conducted the tests on 400 patients who regularly exercised for 90 minutes or more on a treadmill, but did not exhibit any noticeable heart problems.

The study is published in the American Heart Association's journal Circulation.