What is the average weight of a horse heart?

The average resting heart rate for a racehorse is around 28-32 beats per minute. A less fit horse might have a resting heart rate of around 30-40bpm.

At maximum output, a horse's heart rate can reach 230-240bpm. At this rate, the heart will pump 250L/min. This is around 4-5 times the entire blood volume of the horse.