The heart is a hollow muscle with an internal skeleton of connective tissue that creates four separate chambers. The superior chambers of the heart are the right and left atria. These chambers primarily collect blood as it enters the heart and help fill the lower chambers.

The more thickly muscled lower chambers of the heart are called ventricles. These are the primary pumping chambers, the left having a thicker myocardial layer than the right. Vertical walls, composed of connective and muscle tissue, separate the two atria and the two ventricles. These walls are called the interatrial septum and the interventricular septum, respectively.

The pulmonary artery, the aorta, the superior and inferior vena cava, and the pulmonary veins are the largest blood vessels in the heart and are often referred to collectively as the great vessels.