I'll add to hotrodnut's excellent comments - the whole idea behind heel and toe is matching engine speeds on a downshift so that engine compression braking doesn't lock the rear wheels. In road racing, it's an important part of getting the most out of any car and not upsetting the balance/locking the rear end up while turning into a corner - for obvious reasons. Once I learned to do it at driving school, I find that I do it all the time - 20 years now of driving cars on the street and every downshift is with engine speeds matched. It feels awkward to get in a car that has pedals that won't allow it.
The term is a bit of a misnomer in most cars today as you don't really use your heel and toe anymore. You simply hit the brake on the right side of the pedal/left side of the ball of your foot, and then rock/roll your foot to the right (your right knee will actually swing an arc from the steering column towards the center console) - in that rocking it will contact a well placed gas pedal and open the throttle. Practice and it will become second nature - you won't even have to think about it. Most brake pedals can be adjusted a bit closer to the floor. Here's the thing though -- proper adjustment calls for the gas pedal and the brake pedal 1) to be close enough together that the width of your foot at the ball can span them, and 2) they be at roughly the same height WHEN YOU'RE UNDER HEAVY braking. If you set them for the right height under light street braking, then the brake pedal is usually too low under heavy braking resulting in it being easy to hit the throttle accidentally while braking. I can tell you that SIGNIFICANTLY increases stopping distances.
Nice thing about stainless lines, rigid calipers and hard pads is that once the brakes 'hit', pressing harder doesn't move the pedal a lot further down.
Best thing is to do once your pedals are set up correctly is to have someone who can do it show you. Meanwhile, crank the car up (brake pedal height usually changes slightly with the engine running - vacuum power brakes and all) and practice. Brake on with left side of your foot and your knee pointed towards the steering column; arc your knee towards the center console while holding your ankle stiff and the right side of your foot should roll onto the gas pedal causing the engine to rev.
Have fun! By the way - the pedals in the Volvo and my wife's BMW are PERFECTLY positioned for heel/toe from the factory. Funny enough, the last complete Ford I owned, 94 Explorer, had it's pedals perfectly positioned for it too. Go figure. And it's REALLY fun to match revs on the bike - but of course, you don't have to "heel and toe" to do it. Requires a learned right hand technique - squeeze front brake while rolling on throttle - fun!
