THE MAIN FUNCTIONS OF CARDIOVASCULAR SYSTEM ARE TO PUMP BLOOD THROUGHOUT THE BODY.
The main point to focus is that during its pumping what functions are performed by heart?
The following main functions are performed by heart;
1) Transport oxygen from lungs to heart then to all parts of body's cells.
2) Transport carbon dioxide from tissues of all body part to heart then to lungs for expiration(removal of air).
3) Transport of hormones from endocrine glands to their target sites.
4) Transport of nitrogenous waste from tissues to heart then to kidney for their removal.
5) Transports of nutrients from small intestine to liver for metabolism...then the metabolized nutrients are transferred to whole body.
etc
The above mentioned function are perform by cardiovascular system i.e., to complete all these functions HEART, BLOOD VESSELS and BLOOD CELLS are involved.