First draw the heart onto the card board, then add the puzzle parts in the middle. Go over everything in permanent marker and then cut it out using a crafting knife. The pieces should fit together nicely.
Step 1: Tracing and Cutting
After that, get your wood and lay out the separate pieces. Trace around each individual one. Once finished start to cut out your pieces in what ever way is easiest for you, I prefer using a band saw.
Step 2: Sanding
Then continue to sand with either a sanding block or a sanding machine
Step 3: Painting
If you want to you can then paint it how you like or varnish it. (I advise that you you don't want to paint it you varnish it).