Walnuts are excellent for your heart as they are rich in omega-3 fatty acids.
There is some sugar in this recipe, but not much. It translates to about 5/6% of your recommended daily carbohydrate allowance. If you rather avoid sugar, it can be replaced with a lower GI alternative, such as dates or syrups. If using a wet ingredient, be mindful you may need an additional 10-20g of flour.
Cocoa is thought to be quite a nice source of antioxidants called flavonoids, which might play a hand in 'relaxing' blood vessels.