You start by making a nine-patch. Since the swaps were 6" squares, the 9-patch was a whopping 18". Huge! The blocks you place in the corners will not be cut, so that's where the hearts go. The center block will end up smallest, so usually you use something darker there.
Here's my first giant 9-patch.
Then you slice it down the center, both vertically and horizontally.
Then you play with the 4 resulting blocks to find an arrangement you like. Here are some of my possibilities, on my design wall.
If your uncut blocks don't have a definite right way up, the possibilities are doubled, or you can start out with two of them (generally diagonally - but there's no rules here) going the opposite direction.
This is really a fun pattern.