A condition of fullness of the blood vessels in a particular part or in the whole body. This results in a florid, red appearance of the affected area, particularly the face. The volume of blood may be increased (POLYCYTHAEMIA) or the blood vessels beneath the skin may be dilated. Plethoric lung fields are seen on X-rays of patients with left-to-right shunts through the heart wall (see SEPTAL DEFECT).