Heat of passion or sudden passion is any intense, emotional excitement that prompts violent and aggressive action, such as rage, anger, hatred, furious resentment, fright, or terror that would cause an ordinary person to act on impulse and without reflection. When a crime such as murder is committed in the heat of passion and in response to a provocation—as opposed to being premeditated or deliberated—the provocation may serve as a partial defense to the crime by eliminating the premeditation element of a murder charge (also known as malice or malice aforethought), reducing the charge to manslaughter, for example.

The classic example of heat of passion provocation is when a spouse or lover finds his or her partner in an intimate place or sexual act with another person and shoots, stabs, or otherwise kills or attempts to kill one or both of them. The heat of passion defense is only available when the defendant reacts immediately to the provocation and without cooling off. If, for example, the defendant leaves and returns 30 minutes later to kill the cheating spouse, the heat of passion defense may not be available.

And in some states the heat of passion defense may also apply when the defendant had the honest but unreasonable belief he was confronted with deadly force, and used deadly force to defend himself.

Laws regarding the availability of the heat of passion defense vary from state to state. Some state laws downgrade a murder charge to manslaughter when the crime was committed under the influence of extreme mental or emotional disturbance for which there is reasonable explanation or excuse. These laws are generally located in a state’s statutes—often in the penal or criminal code.

And even when a partial defense of heat of passion or extreme mental or emotional disturbance may be available to a defendant, a conviction for manslaughter can carry a lengthy prison term and other serious consequences.

In Pennsylvania, the concept of 'heat of passion' or 'sudden passion' is recognized as a mitigating factor in criminal cases, particularly in homicides. When a person commits a killing in the heat of passion, provoked by circumstances that would cause an ordinary person to become emotionally or mentally disturbed, it may reduce a murder charge to voluntary manslaughter. This is because the element of malice, which is required for a murder charge, is negated by the defendant's impassioned state. Pennsylvania law requires that the provocation be sufficient to overcome the reason of an ordinary person, the defendant must have actually acted under the heat of passion, and there must not have been a reasonable opportunity for the passion to cool. If there is a 'cooling off' period where the defendant had time to regain composure, the defense may not apply. The heat of passion defense is codified in the Pennsylvania Consolidated Statutes, Title 18, which deals with crimes and offenses. Defendants should consult with an attorney to understand how this defense might apply to their specific case and to navigate the complexities of the law.