Heart is a mesodermal organ, present in thoracic cavity between lungs. It is protected by double layered Pericardium with pericardial fluid in it. It has four chambers, 2 atria and 2 ventricles.
Two atria are separated by inter-atrial septum while ventricles are by inter-ventricular septum. Atria and ventricles of same side are separated by atrio-ventricular septum, which are provided with an opening through which the two chambers ( atrium and ventricles ) of same side are connected. Opening between right atrium and right ventricle is guarded by Tricuspid valve while bicuspid valve guard the opening between left atrium and left ventricle. Opening of right and left Ventricle into pulmonary artery and Aorta is guarded by semi-lunar valve. These valve prevent the back flow of blood in heart.