Hawthorn Extract Used in Research HeartCare (TM) contains the actual hawthorn extract used in research studies. It supports efficient heart muscle metabolism by helping improve its oxygen and energy utilization.* 18.75% Oligomeric Procyanidins While many other hawthorn extracts contain vitexin from the plant’s berries, HeartCare is standardized to oligomeric procyanidins extracted from the leaves and flowers for optimal effectiveness.