1. A specialized network of vessels for the circulation of fluids throughout the body tissues of an animal. All animals, apart from simple invertebrate groups, possess a vascular system to enable the passage of a fluid (i.e. blood or haemolymph) around the body to transport respiratory gases, nutrients, excretory products, and other metabolites into and out of the cells. In vertebrates it consists of a muscular heart, which pumps blood through major blood vessels (arteries) into increasingly finer branches until in the capillaries it is in intimate contact with tissues (see microcirculation). It then returns to the heart via another network of vessels (the veins). This closed system of circulation also enables a stable internal environment for tissue function (see homeostasis), the transmission of chemical messengers (hormones) around the body, and a means of defending the body against pathogens and damage via the immune system. Small invertebrates, such as arthropods and many molluscs, have an open circulation system filled with haemolymph, which fulfils many of the same functions as blood (see haemocoel). A water vascular system is characteristic of the Echinodermata.

2. The system of vascular tissue in plants.

https://www.texasheart.org/heart-health/heart-information-center/topics/anatomy-of-the-heart-and-cardiovascular-system/ Interactive round-up of the human cardiovascular system, presented by the Texas Heart Institute