Even Larger Hearts:
One way to upscale your hearts is by using larger yarn, like chunky or bulky yarn with a larger crochet hook, size N or larger.
Another is by adding lager stitches at the middle section of your heart. After your dtr (double treble crochet), do a triple treble by doing another yarn over prior to entering the magic loop. You’ll also need to add ch stitches prior to slst 1 and afterward as well to match the stitches height. You can keep adding larger stitches if necessary, there’s a limit I’m sure, but I haven’t dared try for fear that the crochet gods might smite me.
Ch 2, pull tight, slst into the first sc made.
Cut the yarn and pull through, hide and cut the ends.

Even Smaller Hearts:
To shrink your heart down the best way is by using smaller yarn or even thread. This mini one I made that would be perfect for earrings was made using embroidery thread and a size 1.5mm crochet hook. You can even go smaller using regular thread and an even smaller hook!