the Equus ferus caballus (Domesticated Horse)
The horse has long since been utilized by people for work, transportation, sport, etc. They have a very strong fight-or-flight sense, hence their ability to either flee from a situation quickly or stand their ground, like when they are protecting their young from predators. Horses have been bred differently over the years, being separated into three general categories: Hot-blooded, Cold-blooded, and Warm-blooded. Hot-blooded horses have speed and endurance, Cold-blooded horses are suitable for heavy workloads, and Warm-blooded horses were bred from mixes between Cold and Warm-blooded horses, mainly for riding purposes.
The system
Like humans and other animals of the phylum, horses have a closed cardiovascular system, with the main purpose of pumping blood through the body. Its heart grows larger until it reaches the age of four. Its heart is split into four chambers: The left and right ventricles and atria, having the same functions as a human heart. Size of a horses heart is not directly connected to the horses size, but its heart rate can determine how fit the horse itself is. Heart rates can range from twenty to two hundred and forty beats per minute.