The study found that one or two servings of good-quality chocolate every week lowered middle-aged and elderly women’s risk of developing the condition by almost a third.
Scientists examined the association between chocolate and heart failure in almost 32,000 Swedish women aged between 48 and 83.
Moderate chocolate consumption significantly lowered heart failure risk, although as more or less was eaten, the protective effect was reduced.
Servings of 19 to 30 g eaten once or twice a week led to a 32% risk reduction – which fell to 26% when one to three servings a month were eaten, while one serving a day or more showed no benefit.
A typical chocolate bar weighs around 100 g, but the amount of healthy cocoa solids it contains varies greatly.
Dark chocolate can contain as much as 75% cocoa while standard milk chocolate may have 20% or less.
Antioxidant plant compounds called flavonoids in cocoa are believed to protect against heart disease and high blood pressure.
The study’s authors pointed out that chocolate eaten in Sweden tends to have a high cocoa content.
The findings are reported in the American Heart Association journal Circulation: Heart Failure.