Carbon dioxide can be dissolved in the blood on the right side of heart.
The right side of heart includes the right atrium and ventricle, which then pumps blood to the lungs for gas exchange. With that being said, the blood in the right side of heart are poor in nutrients and full of waste. One kind of has waste include carbon dioxide, and they're also excreted out during gas exchange.
Carbon dioxide are produced during cellular respiration, they're one of the products of the reaction.