Is the heart divided into right and left sides by the aorta

Well no. The heart has four chambers. Right Atrium, Right Ventricle, Left Atrium & Left ventricle. The atria are adjoining each other separated by the Atrial Septum. The Ventricles lie below their respective atria adjoining to each other separted by the inter Ventricular Septum. The Right atrium open into the Right Ventricle via the TRICUSPID Valve. The Left Atrium opens into the Left Ventricle via the Mitral Valve. The Left vetricle opens into the AORTA.

The heart is made of 4 different blood filled chambers, each area is a chamber, 2 chambers comprise each side of the heart, 1 chamber is on top and one chamber is the bottom, 2chambers on top are called the atria, 2 chambers on bottom are ventricles, the left right ventricles are 2 chambers, their job is to squirt blood out to the body and lungs, the middle of the heart is the thick muscle called the septum, the septum separates the left and the right side of the heart,( this is just a rough picture.)

Here is a link to some images showing the heart and the chambers of the heart:
chambers of the heart - Google Image Search (http://images.google.com/images?q=chambers+of+the+heart&hl=en&rls=com.microsoft:en-US&um=1&ie=UTF-8&sa=X&oi=images&ct=title)

The Aorta is posterior to the heart.

The Aorta is posterior to the heart.
The ascending aorta is anterior, the arch of aorta is above and the descending aorta is posterior.