Here's a simple way to think about it:
* Find the withers: This is the highest point of the horse's back, just behind the neck.
* Go down: Move your hand down from the withers, staying in line with the horse's spine.
* Behind the legs: You'll reach a point just behind the horse's front legs. This is where you measure the heart girth.
The heart girth measurement is important for determining a horse's size and for fitting saddles and other equipment.