He nods as Sirius names the spell. "The Heartbreaker, yes." He grimaces. "That's certainly one of them. But there are many more.
"I suppose the sources used in your training were fairly modern, for the most part? If you go back to the age of alchemical research, and filter for the medieval and renaissance preoccupation with demonic forces, you'll find that it was once commonly known--and had been very nearly proven even by today's more stringent testing standards--that any curse, that is, any spell inflicting pain, disease, or healing-resistant disfigurement, stealing life, function, or freedom, or contorting body or personality--was a strain on the soul of the castor more or less proportionate with the distress inflicted on the victim.
"However, as wizards became more and more reviled in and segregated from the muggle population, the preoccupation with souls began to be more and more considered a conceit of muggle religious fanaticism. Furthermore, it was clear (and, I remind you, the prevailing religion at the time was one under the impression that remorse could do most of the work of healing a soul on its own; small comfort for the raped, that) that souls were both far stronger and more flexible than bodies or even minds, and so the question fell out of fashion for quite some time."
He sighs. "Unfortunately, it came back into fashion just about the time when the European world was becoming fascinated by the idea of reincarnation and, due to the Ripper, both fascinated and terrified by the notion of what we'd now call a sociopath. And, of course, in a nearly strictly rational age, particularly on these shores." With a grimace, he finishes, "Ergo, instead of seeking balm for shattered souls, the 'domestication' of the dementors."