Six patients, with surgically implanted tantalum myocardial markers, were trained in deep muscle relaxation therapy. Analysis of individual responses and group means of blood pressure and ventricular dimensions during relaxation showed a decrease in plasma norepinephrine levels and indices of myocardial contractility compared to the control state. Heart rate changes in individuals during relaxation were directly correlated with changes in plasma norepinephrine levels, although group means for heart rate did not change significantly between control and relaxation periods. Base-line plasma norepinephrine levels were directly correlated with systolic blood pressure and were inveresly correlated with a measure of myocardial contractility. These data suggest that physiological changes during relaxation may be mediated through the sympathetic nervous system.