A right-left shunt is a disorder of the blood circulation in which oxygen-poor blood from the venous part of the blood circulation (right half of the heart) enters the arterial part of the blood circulation (left half of the heart) directly, thus bypassing the pulmonary circulation. A right-left shunt can typically occur in the case of heart defects: e.g. due to narrowing of the pulmonary artery, the right ventricle pushes part of the oxygen-depleted blood over the ventricular septum defect into the left ventricle and thus into the systemic circulation. In this case, the pressure in the right ventricle must be greater than in the left. Mixed cyanosis is caused by the mixing of oxygen-rich and oxygen-poor blood.
