Tursaansydän means the 'heart of Tursas' and in Finnish mythology, Tursas (alias Iku-Turso and a few other names) was a rather unpleasant sea-monster that supposedly looked a bit like a bearded octopus. Another name for the same symbol is Mursunsydän, which means 'heart of the Walrus'.
Since Tursas is mythical, we are free to conjure up whatever we wish about the shape of its heart, but we do know some things as fact. One is that the heart of a walrus does not resemble an arrangement of four squares.
Another thing we know (and equally useless general knowledge) is that an octopus has three hearts: two brachial hearts to pump blood through the vessels of the gills, and a further systemic heart to pump blood from the gills through the rest of the body. All three are squishy blobs of heart stuff and none of them even remotely resemble four squares.
So why should the symbol represent the heart of walrussy octopussy Tursas?
There's a clue in the epic Finnish poetry Kalevala, compiled by Dr Elias Lönnrot and published in 1835. (His collection of folk stories is similar to that of the Grimms' Fairy Tales. It is known that Jacob Grimm and Elias Lönnrot communicated with one another.)
In Kalevala's Rune II, we read of 'Wainamoinen's Sowing'. The song starts with Wainamoinen asking Pellerwoinen to sow seeds on the barren earth. Pellerwoinen scatters all kinds of seed everywhere; they sprout and grow into beautiful trees. (Lönnrot, being also a botanist, must have loved this story.) However, the acorn did not sprout and the oak, the "Tree of heaven", was missing from the great garden.
The story continues with mermaids, mowing and raking in a meadow on the seashore, as mermaids do. Then from the ocean, the mighty Tursas emerges, tramples on the mowings which then burst into flames. When the fire dies down, the soil is enriched by the ash and Tursas replants the acorns which grow into mighty oak trees.
So far, Tursas is the good guy of this story.
However, like Jack's Beanstalk and the Tower of Babel, the tree soon reaches the sky. It stretches out its branches above the clouds, hides the sunlight, and very quickly this once-beautiful tree is considered a menace to the true fulfilment of life. The allegory of the story is revealed.
Wainamoinen summons the help of the moon to raise a huge tide (see Marriott's Noah and the 'Ole in the Ark) and uproot the tree. All is well and later the giant Tursas is banished to the depths of the ocean forever.
This folktale reveals an understanding of Tursas' heart. Kalevala does not give any description of the symbol; the following is our own diagnosis based on the story.
Satan can appear just at the moment we need help to do something. Maybe we're not trying to grow an oak tree, but some things in life are challenging and when we see an opportunity that appears to be worthwhile, we naturally grab it.
Swastika superimposed on a cross outline
The solution seems to be a fabulous fit; like the neatly interlocking four squares of the Tursaansydän. We can even see a couple of religious symbols in the design. Big and strong, Tursas seems to know what is needed so we let him get on with it.
But look closely at the four squares, held together by friction. A part of each square is concealed. Something, we don't know what, is being hidden from us. What is the secret? What does the giant not want revealed?
The swastika can represent four branches of an oak tree, spreading out, with each branch supporting a canopy of leaves that block out the sunlight, hiding the truth.
The Tursaansydän described here, then, is a symbol of Satan's cunning deception.
For a long time, especially in Northern Europe, the symbol has been considered a Good Luck charm. The Tursaansydän still appears on stalls selling such trinkets, and people buy them, thinking they will have good fortune. And so the deception continues.
For a challenging view of four squares, see if you can master the Four Square Puzzle
Projekt Runeberg (Finnish)
Rune XLII: 'Capture of Sampo'