Anatomy of the adult heart in section in anterior view and pericardium. The heart provides blood circulation. It pumps blood from the veins to return it to the organs through the arteries. The heart is enveloped by a membrane, the pericardium shown in gray. The heart is a hollow muscle containing two parts separated by a septum, the septum. There is the left heart and the right heart. Each part is subdivided into two chambers, an atrium and a ventricle. Each cavity is separated by a valve shown in gray. The mitral valve separates the atrium from the left ventricle. The tricuspid valve separates the atrium from the right ventricle. Large vessels open into the chambers of the heart. The upper and lower vena cavae open into the right atrium (return of deoxygenated blood). While from the right ventricle opens the pulmonary trunk through the pulmonary valve. From the pulmonary trunk opens the right and left pulmonary arteries to the lungs. The pulmonary veins open into the left atrium (oxygenated blood). As the left ventricle opens the thoracic aorta through the aortic valve to return blood to the organs.