Hawthorn extract for treating chronic heart failure 

This meta-analysis looked at hawthorn as an intervention for heart failure.  Eight trials, which involved 632 patients met the criteria for inclusion.  It was found that hawthorn was more beneficial than placebo in terms of maximal work-load improvement. There was also a significant reduction in pressure heart rate product (systolic blood pressure in mm HG x heart rate per minute/ 100) (n=264 patients).   It was also found that patients had a significant improvement in symptoms associated with heart failure like dyspnea and fatigue. The doses of hawthorn in this meta-analysis ranged from 160 mg to 1800 mg.    

References:

Pittler MH, Guo R, Ernst E. Hawthorn extract for treating chronic heart failure. Cochrane Database Syst Rev. 2008 Jan 23;(1):CD005312.