Traditional herbal medicine, including plants like the Crataegus species (Hawthorn), has been used to treat disease for thousands of years by many different cultures. Shan Zha (Crataegus), the fruit of the species Crataegus pinnatifida (Chinese Hawthorn), is most familiar to practitioners of traditional Chinese veterinary medicine. Shan Zha (Crataegus) is commonly used to treat Food Stagnation and diarrhea and invigorate Blood flow, but studies for treatment of hyperlipidemia, hypertension and other vascular disorders are being performed. There are currently more studies for these latter disorders on a related Crataegus species Crataegus oxyacantha, also known as Crataegus laevigata (English Hawthorn). Crataegus oxyacantha (laevigata) has been shown to be useful to treat cardiac disease, hyperlipidemia and hypertension and to reduce cardiac and cerebral damage, when ischemia and reperfusion occur. The anti-oxidant, antiinflammatory, immunomodulatory, gastro-protective, antimicrobial and anti-anxiety activities of Crataegus oxyacantha (laevigata) may also be clinically useful in the future. The flavonoid components and oligomeric procyanidins, present in the leaves, flowers and berries, are responsible for the pharmacological potential of the herb. Crataegus oxyacantha (laevigata) is safe and adverse side effects are minimal, when consumed in recommended dosages. There are no documented adverse effects associated with low doses, but higher doses can cause hypotension and sedation. Signs of acute toxicity are bradycardia and respiratory depression, which can lead to respiratory paralysis and cardiac arrest. Further investigations to isolate pharmacologically active and clinically important phytoconstituents of the Crataegus species and evaluate long-term safety and drug interactions are warranted.