"Oh Carl... You're breaking my heart! Mom was right..."
Heartbreaker is a low-tier passive Ability available after acquiring the Skill of the same name. It increases the likelihood of scoring a Killshot specifically to the heart by multiplying the basic value of the Critical of the Weapon wielded by three.
A useful skill, but it's rather specific in operation. To achieve the best heart hit rates, it would be best paired up with a Rifle and Anatomy while setting the favourite target to the "Straight to the heart!" If those are not available, it is advisable to pick a firearm that fires multiple rounds in quick succession to increase the likelihood of hitting the heart proper. Other Critical-enhancing skills, such as and Voodoo Doll, can make a huge difference.
If the aforementioned combinations are used in conjunction with CK-Magellan (the quickest semi-automatic rifle), and any aiming skills (e.g Laser Sights, Eye of the Tiger, etc.) the odds to hit the heart can reach enormous levels and every other shot may result in an immediate kill shot, allowing you to quickly dispatch multiple enemies, and turning your unit into an extremely lethal killing machine.
As you can see, the skill is perfect when used in conjunction with other abilities and various weapon types and strategies, but it is mostly inferior, however, when compared individually to many other abilities due to its lower multiplication and requirement to be aiming to a specific target. For example, considering that Hydroshock Shells present the ability to achieve killshots anywhere in the body and is four times as likely to do so compared to only three times as likely with the Heartbreaker, it makes it relatively weak in comparison; although it does not take one of rather valuable Equipment slots.
Still, if quick kills are your game, this skill gives you the means to greatly enhance their number if used properly.