Does heart size vary within a breed?
In Thoroughbreds, some bloodlines seem to produce larger hearts, and a study of over 7000 horses found evidence that young horses with the largest hearts often become above-average performers in their racing careers. Secretariat, Triple Crown winner and holder of several record race times, had a heart almost twice as large as that of the average Thoroughbred. How fast does the horse’s heart beat? The resting pulse rate in newborn foals is about 80 to 100 beats per minute. By the time the foal is several weeks old the rate is about 60 to 80 beats per minute, and this decline continues as the horse grows. A two-year-old’s heart beats about 45 to 65 times a minute, and an adult horse has a resting heart rate of around 30 to 50 beats per minute. Walking, trotting, and cantering raise the rate to around 80, 130, and 180, respectively, and the pulse of a galloping horse reaches a maximum of 220 to 240 beats per minute. Stroke volume (the amount of blood pumped out of the heart with each beat
