According to the study, a couple of chunks is enough to cut high blood pressure and reduce the risk of diabetes, both major risk factors in heart attacks and strokes.
But the scientists stressed that only dark chocolate, made from cocoa rich in natural ingredient flavanols, is good for the heart.
In tests on 19 people, one half who ate just over six grammes a day over fifteen days showed significant falls in blood pressure. But half given white chocolate showed no improvement, reports The Mirror.
Those on dark chocolate saw readings drop from a high 142/90mmHg to 137/87mmHg, a significant decline.
The US and Italian scientists said in the Journal of Nutrition: "It suggests cocoa products may have a positive impact on cardiovascular risks."
Flavanols, present in other plant-based foods such as fruits, red wine, and tea, work by increasing nitric oxide, which lets blood flow freely.