Few things in life are as beautiful as a flower. These two flowers, however, have exactly the same size hearts! If you don't believe me, print it out, and measure them with a ruler.
This works in a similar way to many optical illusions. Since the right hand flower surrounds its heart with larger petals, our brain reports that the right hand flower is the largest - it is. However, the heart on the right is smaller than the petals, and our brain notices this. When we look over to the left hand (smaller) flower, we immediately notice that the heart is larger than the petals. This tricks our brain into giving more importance to the left heart, and consequently we believe this heart to be larger.