When going through my box of trick decks, marked cards, etc, I found two decks together, marked as *Multi*.
Each of them are Svengali cut (in pairs of KC/KS, 3H/3D, etc). One is in suit order, so riffling shows two suits each way, and the other (still in pairs) is in random order.
I have no idea when I bought these, or why. Any idea of a trade name, inventor, routine?
All suggestions welcome.

It could be the Cardiologist Deck.

Thanks for the quick response. Looking at the Cardiologist Deck it certainly sounds like the same set-up. Full deck of 52 cards, can (riffle) shuffle, produce paired card, etc.
However, I have no memory of buying that particular effect.

So, I am left with a couple of questions. Why TWO decks? Why did I label them "Multi"? And where did I get them?

Perhaps "Multeffect Cards", by Val Evans? Jinx p177. Tamariz has donde extensive work on this deck.

Or possibly Vincent Hedan’s version of the above. I believe he calls his a Multieffect Deck