When blood leaves the left side of the heart it is full of?

Blood entering the right atrium is full of carbon dioxide; that is, it is deoxygenated. From there it enters the right ventricle and is pumped to the lungs, where the carbon dioxide is exchanged for oxygen via the process known as respiration (simply put, breathing). The now-oxygenated blood returns to the left atrium of the heart, progresses to the left ventricle, and is pumped throughout the body before returning go the right atrium.