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 Delaware, 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 crime such as murder under the influence of a strong emotional state, such as rage or terror, without premeditation, it may reduce the severity of the charge from murder to manslaughter. This is because the emotional state can negate the element of malice aforethought, which is required for a murder charge. Delaware law acknowledges that an ordinary person might act impulsively under certain provocative circumstances, and thus, the law provides for this partial defense. However, for the defense to be applicable, the reaction must be immediate and without a 'cooling off' period. If there is a significant delay between the provocation and the act, the defense may not be available. Additionally, Delaware may consider the defendant's honest but unreasonable belief of being threatened with deadly force as a factor. The specifics of how this defense is applied can be found in Delaware's penal or criminal code, and even if successful, a manslaughter conviction can still result in a significant prison sentence and other serious consequences.