The paracardiac blood pump is destined for protruding through the cardiac wall into the heart with a portion of its housing (10) and for suctioning blood from the heart. The blood is pumped into one of the blood vessels connected with the heart through a line that extends outside the heart. A cannula (30) is arranged in front of the inlet (17) of the pump ring (16). The housing (10) and the cannula (30) have approximately the same outer diameters of 13 mm at most. The housing, together with the cannula (30), can thus be inserted into the heart through a puncture hole that is produced in the cardiac wall without removing material.