Hearts and arrows diamonds are a rare and special type of round diamond. The name, hearts and arrows, refers to the pattern that is visible in such a round diamond, with the hearts being seen from the bottom and the arrows from the top. Only the arrows of this pattern are, however, visible to the unaided eye, and remain visible after the diamond has been set. The hearts of the hearts and arrow pattern can only be seen when the diamond is loose and viewed through a firescope.

The hearts and arrows patterning is the result of perfection in symmetry and proportion in the diamond's cut. In order for the pattern to appear in the correct form with sharp focus, the facets must be perfectly aligned with one another. The arrow pattern is formed as a result of the main pavilion facets being aligned perfectly so that any given main pavilion facet is reflected by the main pavilion facet directly opposite to it. The arrows pattern is seen when viewing the diamond from the table down, and is more prominent when viewed through a FireScope. The hearts pattern is formed when pavilion facets are reflecting one another, while the crown facets are also aligned to perfectly reflect one another.

The result of perfect symmetry in a diamond that has been cut properly is that it is capable of reflecting 98% of the light entering it. This level of light reflection is why the hearts and arrows type of diamond is known as a "super ideal cut", as opposed to those diamonds known as "ideal cut". This is not to say that all super ideal cut diamonds are hearts and arrows, however. Some of the finest in ideal and super ideal cut diamonds are not hearts and arrows diamonds. It is only a small percentage, about 1 tenth of 1% of all diamonds that can even be used for true hearts and arrows type diamonds, due to the tremendous symmetry requirement to achieve the proper hearts and arrows effect.

AGS, American Gemological Society, has a diamond grading for super ideal cut known as AGS"000"or Triple 0. Many mistakenly believe that this automatically indicates that a diamond is a hearts and arrows diamond. This is not the case, however, as AGS does not look for the hearts and arrows patterning, but simply gives a grade of 0 in three categories: cut, polish, symmetry. This indicates perfection in all three of these categories for a particular diamond.

Where the misconception occurs is in that most think that perfection in the three categories automatically indicates that the hearts and arrows patterning must appear, and appear in a sharp and clear focus. This is not always possible, and some "000" diamonds do not display clear hearts and arrows. It is for this reason that a hearts and arrows diamond will be notably more expensive than the same size diamond that does not display the proper hearts and arrows patterning, even should both be AGS "000" diamond grade. Much of the greater expense is due to the greater expenditure of time and effort in order to achieve the hearts and arrows patterning, taking up to 100 times as much time to produce.

The hearts and arrow diamond actually finds its origins in the firescope itself. In the late 1970s and early 1980s, the Japanese developed the FireScope as a tool designed to evaluate the overall quality of diamonds in relationship to one another. It was Takanori Tamura who first noticed the patterning that he saw as a mandala, or the Buddhist 8-spoked wheel of life, and which we recognize as a series of 8 hearts and 8 arrows.