Hawthorn (Crataegus species) has been used to treat heart disease as far back as the 1st century. By the early 1800s, American doctors were using it to treat circulatory disorders and respiratory illnesses. Traditionally, the berries were used to treat heart problems ranging from irregular heartbeat, high blood pressure, chest pain, hardening of the arteries, and heart failure. Today, the leaves and flowers are used medicinally, and there is good evidence that hawthorn can treat mild-to-moderate heart failure.