CHICAGO — Using cocaine can damage the heart's smallest vessels, but this problem doesn't show up on routine medical tests, according to a new study .

"We see many emergency room admissions because patients experience chest pain following cocaine use," said study researcher Dr. Varun Kumar, an internist at Mount Sinai Hospital in Chicago.

However, a test such as an angiogram that looks at blood flow in the heart's main arteries would appear normal, leaving doctors without an explanation for the chest pain, Kumar said. [Heart of the Matter: 7 Th...our Ticker]

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In the new study, Kumar and his colleagues looked at the function of the heart's small vessels in people who had come to the hospital because of chest pain, including 210 people who did not use cocaine and 202 people who said they had used the drug.

The results showed cocaine users had abnormal blood flow in the heart's small vessels, a condition that puts them at risk for heart problem or even death, according to the study presented here today (Nov. 18) at the meeting of the American Heart Association.

In cocaine users, the small vessels were over-dilated, resulting in faster blood flow. The abnormalities were still clear even when comparing cocaine users to nonusers who had diabetes or high blood pressure. Smoking habits were also unable to explain the difference between groups, the researchers said.

The findings suggest that even when there's no sign of damage to the arteries, cocaine users may have damage in their small vessels, leading to symptoms such as chest pain and shortness of breath.

Previous studies have found that cocaine, even if used only socially, can cause heart attacks in young, healthy people. The drug can damage the body's large arteries such as the aorta, causing stiffness in the vessels. As a result, blood pressure increases and the heart has to work harder.

In the new study the researchers didn't look at how often patients had used cocaine.

More research is needed to find how to prevent heart disease in people who use cocaine but are otherwise healthy, Kumar said. For example, these people may benefit from therapies aimed at preventing heart disease, such as aspirin and cholesterol-lowering drugs, he said.

"We need more research on this, but there's some evidence to suggest cocaine itself can stimulate clot formation and may contribute to atherosclerosis and coronary artery disease," Kumar said. Atherosclerosis is the build-up of plaque in the arteries, and coronary artery disease is the narrowing of the blood vessels that supply blood to the heart.

"Cocaine use is prevalent, and we don't want these patients to fall through the cracks," he said.

Email Bahar Gholipour. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.