The leaves, flowers, and berries of hawthorn contain a variety of bioflavonoids that appear to be primarily responsible for the cardiac actions of the plant. Flavonoids found in hawthorn include oligomeric procyanidins (OPCs), vitexin, vitexin 4’-O-rhamnoside, quercetin, and hyperoside. These compounds are often standardized in leaf and flower extracts, which are widely used in Europe.

Hawthorn is thought to exert many beneficial effects on the heart and blood vessels. These include improved coronary artery blood flow and strengthening of the contractions of the heart muscle.¹ Hawthorn may also improve circulation to the extremities by lowering the resistance to blood flow in peripheral blood vessels.² The bioflavonoids in hawthorn are potent antioxidants.³ Hawthorn extracts may mildly lower blood pressure in some people with high blood pressure but should not be thought of as a substitute for cardiac medications for this condition.

Clinical trials have confirmed that hawthorn leaf and flower extracts are beneficial for people with stage II (early-stage) congestive heart failure.^{4, 5, 6, 7, 8} People with congestive heart failure taking 160–900 mg of hawthorn extract per day for eight weeks showed improved quality of life including greater ability to exercise without shortness of breath and exhaustion. Congestive heart failure is a serious medical condition that requires expert management rather than self-treatment. One study has shown that hawthorn leaf and flower extract may also help those with stable angina.⁹