Blood with a low oxygen content and high carbon dioxide content that is on its way back from tissue towards the heart and the lungs. Between peripheral tissue and the lungs, it is found in the veins, between the heart and the lungs in the pulmonary artery. The low oxygen content make it dark red in colour.

Venous blood is sampled for most medical blood tests. Typically, the easily accessible jugular vein is used for obtaining a blood sample.