Often students mistake the pulmonary artery for the aorta. The pulmonary artery, or pulmonary trunk, is the most anterior vessel found on the heart; it is indicated below with a blue pencil. The aorta lies behind the pulmonary trunk, indicated with the red pencil.
When the heart is dissected, the path of blood through the pulmonary artery and the aorta can be visualized using the pencils as markers. Blood flowing out of the pulmonary artery will travel to the left and right lungs. Blood travelling out the aorta will deliver blood to all of the body tissues. The contraction of the left ventricle is a very strong contraction called ventricular systole, which must be powerful enough to send blood out the aorta and to the body, and then get the blood back to the heart through the veins. This is why the wall of the left ventricle is thicker than the walls of the right ventricle.
The photo shows the aorta’s location as it leaves the left ventricle, and the location of the pulmonary artery which connects to the right side of the heart. Beginning anatomists are advised to determine the left and right side of the heart by the thickness of the ventricle – the left side is much thicker. It is also interesting to note that the pulmonary and aorta vessels cross each other.