Eating high levels of chocolate could reduce the risk of coronary heart disease and stroke, according to a review of previous research.
Data from 114,009 patients suggested risk was cut by about a third, according to a study published on the BMJ website.
But the researchers warned that excessive consumption would result in other illnesses.
The British Heart Foundation said there were better ways to protect the heart.
The analysis, conducted by scientists at the University of Cambridge, compared the risk to the brain and heart in groups of people who reported eating low levels of chocolate, fewer than two bars per week, with those eating high levels - more than two bars per week.
It showed that the "highest levels of chocolate consumption were associated with a 37% reduction in cardiovascular disease and a 29% reduction in stroke compared with the lowest levels".
One of the researchers, Dr Oscar Franco, said chocolate was known to decrease blood pressure.
He told the BBC the findings were "promising", but needed further research to confirm any protective effect.
The study also warns that chocolate can lead to weight gain and Type 2 diabetes. It suggested that chocolate could one day be used to protect from heart problems and stroke - if the sugar and fat content of chocolate bars was reduced.
Dr Franco added: "The advice if you don't eat chocolate is not to start eating chocolate."
For those who did eat chocolate, he recommended that they should "avoid binge-eating" and eat "small amounts [of chocolate] on a regular basis".
Victoria Taylor, senior heart health dietician at the British Heart Foundation, said: "Evidence does suggest chocolate might have some heart health benefits but we need to find out why that might be.
"We can't start advising people to eat lots of chocolate based on this research.
"It didn't explore what it is about chocolate that could help and if one particular type of chocolate is better than another.
"If you want to reduce your heart disease risk, there are much better places to start than at the bottom of a box of chocolates."