Exercise training improves heart rate variability in older patients with heart failure: a randomized, controlled, single-blinded trial.
Murad K, Brubaker PH, Fitzgerald DM, Morgan TM, Goff DC, Soliman EZ, Eggebeen JD, Kitzman DW. Exercise training improves heart rate variability in older patients with heart failure: a randomized, controlled, single-blinded trial. Congest Heart Fail. 2012 Jul-Aug; 18(4):192-7.