Most of this process is pretty simple if you are familiar with working with paths. However, there are a few tricks to the alignment and combining that you need to know in order to get the right results. Open-ended paths and paths for which the wrong combining mode are selected for do not produce the proper results. Photoshop will first close the ends of the open paths and then combine the shapes. This may lead to some unexpected results.
Alignment has to be perfect for the shapes to combine, unless you provide an overlap. If you don't overlap and alignment isn't perfect, you'll still get one shape when you combine; but it may have some faults, such as a very thin space between the halves (this may look like a center line).
For example, if you make a heart quickly, you can create an overlap that will make sure the shapes combine instead of worrying too much about perfect alignment. This overlap will extend beyond the center line (see Figure 5).
Creating an overlap probably won't be necessary for such a simple shape, but more complex shapes might require more complex handling, including overlaps.
If you highlight both "halves," you can combine the two as a single shape, exactly as shown in the steps. However, the end result will cover over any slight misalignment and ensure that the shape is whole.
If you choose to overlap, make the overlap changes to one-half of the path set after you have already made the duplication. Having both halves in place will help you see what needs to be overlapped more exactly. When the overlap is complete, delete the guide, reduplicate, and reposition, just to be sure everything is aligned and shaped correctly. This way, you can be sure you have perfect symmetry.