Now let's begin by discussing what the structure of the heart is. Now the heart is an organ that is located inside a protective covering, a protective active sac we call the pericardial sac or simply the pericardium. Now, as we'll see in just a moment, the pericardium actually consists of two different layers. And the function of the pericardium is not only to protect the heart from physical damage, it's to also lubricate the heart and it's to also attach the heart to other parts of our body. So to actually examine what the pericardium looks like, let's take a cross section of the heart. We get the following diagram.