- Heart disease is the leading cause of death in the United States. Eating fruits and vegetables with chemicals called flavonoids may protect against heart disease and improve blood flow to the heart. They are found in blackcurrant berries. Oils found in fish and mussels called omega-3 fats have also been shown to protect the heart. Researchers want to know if blackcurrant extract and omega-3 fats can improve blood flow, which may increase blood to the heart. They also want to learn about the health of blood vessels and how the heart works.