The research will lend further weight to the various health claims now attached to the traditional indulgence.
Dark chocolate has recently been making inroads into the health market as its beneficial antioxidant and flavanoid content becomes more widely publicised and consumers switch from milk or white chocolate to keep up with the trend.
Scientists at the John Hopkins University School of Medicine say that a few squares of chocolate a day can reduce the risk of a heart attack by almost 50 per cent in some cases.
The discovery came after volunteers for a trial on the effects of aspirin were disqualified for eating chocolate, despite being warned that this would interfere with results from the study.
Despite being barred from participating in the drug study, the chocolate-eaters blood was examined and compared with others who hadn't indulged in order to determine what effect cocoa has on platelets.
Platelets from those who had eaten chocolate clotted more slowly than those who had not - taking an average of 130 seconds to clump together compared to 123.
Professor Diane Becker 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."
She continued: "Eating a little bit of chocolate or having a drink of hot cocoa as part of a regular diet is probably good for personal health, so long as people don't eat too much of it, and too much of the kind with lots of butter and sugar."
The full results of the study were presented to the American Heart Association's annual Scientific Sessions in Chicago yesterday.