I realised that I did a MISERABLE job of explaining how I put the heart into each slice of my rosette cake so I took a few more pictures. This is based out of the Great British Bake Off book 'Showstoppers' although I noticed in that that there are very few photographs on how it was done so I found my own technique which worked OK I think....
Tint the marzipan with colour- this will take quite an amount of time, even with good quality gel food colouring (don't use liquid colouring, it will leave the marzipan too sloppy). When the colour is evenly distributed, roll the marzipan into a sausage. Mould into a point at one end and the two rounded parts of a heart at the other.
To make the two rounded parts I cut a line through the sausage with a sharp knife then carefully teased the two sides out to make the heart shape- like this photograph below.
This is only a small segment of the full ring that I did. I put a layer of buttercream on my bottom layer. Pressed the moulded heart ring into the buttercream then top with more buttercream to cover the marzipan. Put on your top layer and voila! A really effective cute touch to any cake that is really not that hard!