A randomized controlled trial of a controlled breathing protocol on heart rate variability following myocardial infarction or coronary artery bypass graft surgery.

Objectives: To determine whether a controlled breathing programme increases heart rate variability following an acute myocardial infarction and/or coronary artery bypass graft surgery.

Rationale: Heart rate variability is reduced following a myocardial infarction, and low heart rate variability is associated with a high mortality risk. By changing tidal volume and rate of breathing, individuals can alter beat-to-beat heart rate variability.