The study of more than 19,000 people, published in the European Heart Journal, found those who ate half a bar a week had lower blood pressure, while nibbling on just one square of chocolate a day can cut the risk of heart attacks and strokes by 39 per cent.
But heart campaigners have also warned that too much is damaging because it is high in calories and saturated fat – two of the key risk factors for heart disease.
Researchers in Germany looked at the chocolate consumption of people aged between 35 and 65 for a decade.
They found that those who ate the most amount – an average of 7.5g a day – had lower chances of heart attacks and strokes than those who ate the least amount (1.7g a day on average).
The difference between these two groups was just 6 grams a day, equivalent to one small square of chocolate a day.
However, Dr Brian Buijsse, from the German Institute of Human Nutrition, who led the research, warned people against eating too much chocolate and putting on weight or cutting down the amount of healthy foods they eat.
"Small amounts of chocolate may help to prevent heart disease but only if it replaces other energy-dense food, such as snacks, in order to keep body weight stable," he said.
Victoria Taylor, senior heart health dietician at the British Heart Foundation, said: "This sounds like a dream for chocolate lovers and just in time for Easter too, but it's important to read the small print with this study.
"The amounts consumed on average by even the highest consumers was about one square of chocolate a day or half a small chocolate Easter egg in a week, so the benefits were associated with a fairly small amount of chocolate."