Researchers at Hope College in Holland., MI, had 71 people mentally relieve hurtful memories. They gave them the choice of forgiving the person or holding a grudge. The researchers found that forgiving the person reduced the participant's heart rates and blood pressure by two and a half times vs. the person's who chose to hold the grudge.
Holding a grudge caused the participant's to sweat while forgiveness left them feeling calm and in control. Since sustained anger and hostility are risk factors for heart disease, forgiveness may be the way to stop these risk factors in their tracks.
Another study published in Psychosomatic Medicine reported testing newly married couples when they had 30-minute discussions and then again 24 hours later. The partner, who used negative fighting styles, including dismissal and disapproval, had significant and undesirable changes in levels of natural killer cells and white blood cells. All these indicated a diminished immune system. The partner who argued more constructively showed little change in their immune system 24 hours later.
So...to forgive and forget. It's your choice!