The term 'Hearts and Arrows cut' is given to diamonds with Excellent cut grades that show a perfect optical symmetry. When viewed from above, the 'crown', the pattern is a series of eight arrowheads. From below, the 'pavilion', the pattern appears as eight heart shapes. This much sought after characteristic is only seen in the highest grade of diamonds.
To be able to see this symmetrical pattern, Hearts and Arrows viewers are used to eliminate incoming light from certain angles and cause the pattern to appear in UV light.
The image to the right is an example of how we grade hearts and arrows: