Language is a tricky thing. Its development is fluid and often lost in the mists of time. Why do we say what we say? Words have origins that are sometimes traced readily, but at other times defy explanation. This is often even more true of sayings and expressions. It can seem a veritable pandemonium.
By the way, where do we get the term pandemonium? If it sounds Latinate to you, you're on the right track, but in fact pandemonium is a place name, used by English poet John Milton, as the place Satan and his peers have their headquarters. So, if you use the term pandemonium today to mean a place of discontent, disquiet, or chaos, your heart is in the right place.
Where do we get the expression, the 'heart is in the right place?' I'm assuming that most people's hearts will be where they have come to be placed - in the middle of the torso, between the lungs and above the liver. The ancient Egyptian mummifiers might have known where the heart was (although they didn't quite know what the organs did), but through the ages the results of the heart beat might bring one to question its location - when it is in the right place, all is presumably well.
Author Webb Garrison has pulled together literally hundreds of words and expressions that might have colourful and interesting backgrounds. This book is a trivia treat - it is not a systematic treatise or etymological survey by any means, but rather a short, handy reference for those who like to ponder imponderables. For those who do any public speaking, this can be a valuable resource.
For anyone else, this is an interesting collection of possible word and phrase origins. I say 'possible', because while Garrison provides a nice bibliography, there are no source citations, and, language being what it is, these phrases may or may not all have the origins presented here. However, a random sampling check against the OED shows that most conform to the most commonly held ideas, at least according to that standard text.
So, follow the hype and get your ducks in a row, for you've heard it here first, though perhaps not from the horse's mouth. It is no hogwash, and I'm not pulling your leg or trying to pull a fast one. I've no axe to grind nor a chip on my shoulder compelling me to recommend this book.