Literary data are interpreted as regards the presence and the rôle of direct neural influences on the ventricular myocardium. It is concluded that the sympathetic system is the most important outflow channel for the effect of psychic functions as regards the ventricular muscle. The intact heart is also greatly dependent on adrenergic mechanisms for the regulation of its contractile performance. Since the metabolic and mechanical effects of sympathetic stimulation are present in the myocardial cell only during contraction, the heart rate in itself is an important determinant not only of the effective inotropic stimulation but also of the enhancement of the local coronary blood flow. Under physiólogical conditions, in the absence of strong emotional stimuli and/or muscular exercise, the heart rate of man and higher mammals is modulated by changes of the vagal cardioinhibitory tone. Experimental data in man and in macaques are presented in favor of the assumption that comparison of beat-to-beat changes of cardiac cycle duration and maximum repolarization vector magnitude may give insight into the presence or absence of sympathetic ventricular activation under given heart-rate-changing conditions.