Blood in the pulmonary circulation exchanges carbon dioxide for oxygen in the lungs through the process of respiration. This circulation consists of the systemic circulation to and from the body and the pulmonary circulation to and from the lungs. The heart functions as a pump in the circulatory system to provide a continuous flow of blood throughout the body. These are surrounded by a double-membraned sac called the pericardium. The left heart has two chambers: the left atrium, and the left ventricle, separated by the mitral valve.The heart wall is made up of three layers: the inner endocardium, middle myocardium and outer epicardium. The right heart consists of two chambers, the right atrium and the right ventricle, separated by a valve, the tricuspid valve.

The wall of the heart is made up of three layers: epicardium, myocardium, and endocardium. The heart is enclosed in a protective sac, the pericardium, which also contains a small amount of fluid.

Commonly the right atrium and ventricle are referred together as the right heart and their left counterparts as the left heart.] Fish, in contrast, have two chambers, an atrium and a ventricle, while reptiles have three chambers.In a healthy heart blood flows one way through the heart due to heart valves, which prevent backflow. In humans, other mammals, and birds, the heart is divided into four chambers: upper left and right atria and lower left and right ventricles. In humans, the heart is located between the lungs, in the middle compartment of the chest. Blood provides the body with oxygen and nutrients, as well as assists in the removal of metabolic wastes.

The heart is a muscular organ in humans and other animals, which pumps blood through the blood vessels of the circulatory system.

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