Draw a labelled diagram showing the internal structure of the human heart.

(N/A) The human heart is a muscular organ that pumps blood throughout the body. Its internal structure consists of four chambers: two upper atria and two lower ventricles.
Key components include:
$1$. $Aorta$: The main artery carrying oxygenated blood to the body.
$2$. $Vena$ $cava$: Large veins returning deoxygenated blood to the right atrium.
$3$. $Sino-atrial$ $node$ $(SAN)$: The natural pacemaker of the heart.
$4$. $Atrio-ventricular$ $node$ $(AVN)$: Relays electrical impulses from the atria to the ventricles.
$5$. $Chordae$ $tendineae$: Fibrous cords that anchor the heart valves.
$6$. $Bundle$ $of$ $His$: Part of the cardiac conduction system.
$7$. $Interventricular$ $septum$: The wall separating the left and right ventricles.
The provided diagram illustrates these structures clearly.