Tai chi can enhance sleep stability in patients with chronic heart failure. Researchers analysed 24-hour continuous ECG data obtained in a clinical trial of tai chi in 18 patients with heart failure. At 12 weeks, those who participated in tai chi showed a significant increase in EEG parameters that indicated improved sleep stability. These improvements were correlated with better disease-specific quality of life and could lead to a decrease in blood pressure and likelihood of arrhythmia. (Enhancement of sleep stability with Tai Chi exercise in chronic heart failure: Preliminary findings using an ECG-based spectrogram method. Sleep Med. 2007 Aug 2 1Epub ahead of print]). Another study carried out in 52 patients with chronic heart failure found that although objective measures of exercise tolerance did not improve significantly with tai chi, patients who did tai chi showed improvement in symptom scores of heart failure and depression, compared with patients in the control group. (An evaluation of the effects of Tai Chi Chuan and Chi Kung training in patients with symptomatic heart failure: a randomised controlled pilot study Postgrad Med J. 2007 Nov;83(985):717-21).