In this survey an extended definition of shunts is given: ‘A shunt is a normal or abnormal passage in between two vessels or vascular areas, which bypasses either a capillary bed, a heartpump, or both.’ Based on this definition a classification of the existing right-to-left and left-to-right shunts in the is evolved. Besides this classification, two forms of recirculation are described, defined as a situation in which part of the bloodflow returns by shunting to its own ventricle. At the same time a survey is given of the various methods of shunt detection. The purpose of this classification is that it can be used for clinical purposes. By confronting the clinical signs and symptoms with suitable ‘physiological’ and ‘anatomical’ techniques, it will be possible in many cases to arrive at a diagnosis during life.