The findings of the manual extrathoracal stimulation of the heart (precordial thump) among 50 persons, healthy individuals and patients with pacemakers, are reported. By all persons it was possible either to cause "extrasystoles" through single blows or to maintain a continuous heart action through a rhythmic stimulation up to 6 minutes ("Temporary stimulation"). Through a manual overstimulation the basic rhythm could be blocked out. -To induce a depolarisation through a thump the locally induced pressure or tension on the heart muscle is of primary importance. For this to occur, the precordial chest thump must develop a rise in pressure of at least 15 to 20 mm Hg in the right ventricle. The location at which the precordial thump can best be effective is on the left border of the sternum in the lower third. That is the region where the heart (right ventricle) is nearest to the chest wall. -Subjective or objective side effects were not observed during our investigations and--in particular--there were no ectopic rhythm or conduction disturbance. -The precordial thump is of importance not only as "initial blow" at the beginning of cardiac resuscitation but also in form of the temporary stimulation in various causes of asystole. It was demonstrated that the manual stimulation of the heart has the same effect as the electrical stimulation and can be used by certain patients by themselves.