Dark chocolate may be just what the doctor ordered, according to a new study out today, which reveals that eating a few squares every day can improve the health of your heart.

The chemical in cocoa beans has a similar biochemical effect to aspirin and can reduce the likelihood of blood clotting, researchers at the Johns Hopkins University School of Medicine and Bloomberg School of Public Health in the US have found.

They have published the results of what is believed to be the first biochemical analysis to explain why eating a small amount every day can almost halve the risk of heart attack death in some men and women by decreasing the tendency of platelets to clot in narrow blood vessels.

The scientists made the discovery when 139 people were disqualified from a larger study looking at the effects of aspirin on blood platelets. These "offenders" had been told to to refrain from indulging in a number of foods known to affect platelet activity, including chocolate. But they could not break their habit.

Diane Becker, a professor at Johns Hopkins, said: "What these chocolate 'offenders' taught us is that the chemical in cocoa beans has a biochemical effect similar to aspirin in reducing platelet clumping, which can be fatal if a clot forms and blocks a blood vessel, causing a heart attack."

The so-called Genetic Study of Aspirin Responsiveness (GeneSTAR) was conducted at Johns Hopkins University between June 2004 and November 2005 and involved more than 500 men and 700 women participants nationwide. None of the "offenders" had previous histories of heart problems, such as a heart attack, but all were considered to be at a slightly increased risk of heart disease because of family history. Fifty per cent of women participants were postmenopausal.