Images of a horse's heart. This amazing pump can easily go from 30 beats per minute up to 240 beats per minute. Notice the thick muscular walls that need to be able to pump blood around the horse's entire body. A average horse heart weighs about 8 lbs and can squeeze out 1 quart of blood with each pump.
The cardiovascular system of a horse consists of a pump (the heart), a distribution system (arteries), exchange areas (capillary beds), and a collection and return system (veins).
The heart of a 1,000-pound adult horse is about the size of a large melon and weighs about 10 pounds.
The left heart collects blood returning from the lungs via the pulmonary veins and pumps it to the body via the aorta. The right heart collects blood returning from the body via the large veins and directs it to the lungs via the pulmonary artery. The output of each ventricle in an adult horse at rest is about 25 to 40 liters/minute (approximately 7 to 10 gallons), compared with four to five liters/minute in an average adult human (1 liter equals about 1.05 quart).
Cornell: Rooney's guide to the Dissection of the horse - Great Detail !
Example of Head Dissection: