It is written in UK terminology:
UK dc : US sc
UK tr : US dc
I have made the two parts in contrasting colours to show some of the steps more clearly.
It all starts with a humble straightforward 2 rounds granny square.
Then another modified row is added to one side:
slip stitch into the corner space;
chain 3, 1tr in corner space;
chain 1;
3tr in middle space;
chain 1;
finally 2 tr in next corner space.
Turn.
Chain 2;
6tr in middle stitch of 3 treble group of previous row;
Chain 2;
slip stitch into the top stitch of the 3chain of the previous row.

Finish off.
Make two of these half heart shapes,
one with a short end of wool and one with a long strand for sewing the two parts together.
Weave in the starting thread of yarn.
Place the half with the short end at an angle with the wrong side up.
Place the second half on top, right side up, with the long tail towards the right.
The points should line up.
Sew the two shapes together down towards the point and then up the other side
(I have used a tapestry needle and an over stitch taking in both loops on both sides).
You may need to thread the strand through a couple of stitches before you start, as the place where you finished off is a little higher than the first stitches where the two shapes meet.
The next part probably sounds more complicated than it actually is - once the two parts are partly sewn it should happen naturally - but here goes!
The third edge to be sewn is where the side edge of the top shape (multi-coloured) meets the top edge of the second granny round of the bottom shape (pink).
The modified extra granny row of the bottom shape stands above the join.
Some of the stitches are straight forward to join:
for others I threaded through the treble loops of the row above:
Finish off at the end of the row and thread the end through the stitches you have just made, hiding the end inside one of the trebles.
Finally thread the short end from the first shape down the side seam towards the point.
The fourth side of each shape forms the opening!
So in summary (or the short version!)
Hook a two round granny square, ss into corner space then
Chain 3 1tr in corner space; ch1; 3tr in 2nd space; ch1; 2tr in 3rd space.
Turn
Ch2; 6 tr in middle tr of previous row; ch2; ss in top pf ch3 of previous row. FO.
Make 2 - one with a short final thread and one with a long one.
Weave in starting ends.
Place the half with short end wrong side up on the bottom, put the other half, right side up, on top lining up the points. Join two of the sides by sewing down to the point and up using a tapestry needle.
Stitch the third side, finish off and weave in ends.
Hope it all makes sense - my patterns are usually scribbled in my own code and tweaked as I go along!
I have already started making more for the
heartsease project