We are not discussing low heels here. Heels can be low, but they are not necessarily at incorrect angles or position.
A simple first step, easy for the owner to orientate themselves as to heel position, is by taking an imaginary line following the coronet angle and extending out until it passes the forelimbs of the horse. Basically, if that line falls anywhere above the knee the heel is underslung.
The red line shows were the heel currently is and the blue indicates the widest part of the frog, and where the heel should be.
And what are they running from? The heel takes the most stress, doing the most work to protect the internal structures consisting of the DDFT, Digital Cushion and more - like the suspension on your car - yet it is the weakest part of the hoof capsule and so, if not correctly maintained, it can very easily run away from it´s duties. A migrated heel is not working!
Here is one of my stunning foundation Appaloosa´s (EV Kaver Onyx Heart), who apart from conformation to die for, enjoys optimum hoof health with her heels correctly positioned - see white line! And of course a close up of those healthy hooves....