Hawthorn is a fine heart and circulatory tonic. It can help lower blood pressure (or, paradoxically, raise blood pressure that is too low) and slow the heart rate and it is used by herbalists in the treatment of angina, cardiac arrhythmia, or a weak or failing heart. The flavonoids and condensed tannin phlobaphene help to dilate the blood vessels, particularly those that supply blood to the heart, while the cyanogenic glycosides have a sedative effect, slowing the heart rate.