Abstract: The invention relates to a blood withdrawal cannula (4) for connecting a pump (2) assisting or replacing activity of the heart to the inner volume of a heart ventricle (1), in particular the left ventricle. At the end thereof that is located in the ventricle the cannula has a pressure sensor (7a, 7b) for measuring the ventricle pressure and/or ventricle pressure differences and at the same end of the cannula has a volume sensor (3a, 3b, 5, 6) for measuring the volume and/or volume changes of the ventricle (1) in at least a partial region of the ventricle. The invention further relates to a measuring device for monitoring the ventricle contractions and/or the function of a pump replacing or assisting activity of the heart. The measuring device can be/is connected to the pressure sensor (7a, 7b) and to the volume sensor of a blood withdrawal cannula according to any one of the preceding claims and is designed to detect pressure changes and volume changes of a ventricle (1) as the heart is beating.