Additional systems must be in place to serve this purpose in larger organisms, and they do so in varied ways.
Earthworms have a system similar to mammals as they have vascularisation (blood vessels), and transport gases dissolved in the blood which is pumped by 5 “hearts”.
Unlike other organisms, they… well, they have 5 hearts!
Insects do not carry respiratory gases in the blood, and have an open circulatory system. Their heart is towards the back of the body (dorsal) and has a tube shape.
An open circulation system means that there is no “blood” flowing enclosed into vessels. Instead, the heart pumps a fluid which is a mixture of blood contents and interstitial fluid (tissue fluid between cells) throughout the head and body, which then returns to the heart as it relaxes. This fluid is called…