Select the middle heart layer (Copy of vector 1) on the Layer palette. Select the shape with the Pick tool. Select Propertiesfrom Tool Options. Change stroke to 3, stroke color to white. Change line style to "Opposing Arrowheads Overlap". Click OK. You should now have a lacy-looking white pattern in center red as shown in the image above.
You may have a gap in the "lace" pattern at the top of your heart (dimple). We'll touch this up using the Paintbrush. First, convert this layer to raster layer ( Layers > Convert to Raster ), then touch up any pattern flaws by adding a few white pixels with a small brush in the area outlined in the screen shot. Zoom in if you need to see better.
Next, click the "eye" button on the layer palette to show the top heart layer (copy 2 of vector 1), Select the top heart with Pick tool. From Tool Options, select Properties. Change stroke width to 7. Click OK.
Note: If the Properties dialog is showing white for stroke color, you forgot to select the top heart first. The heart should be red!
Also convert this layer to a raster layer.