Under and around the left breastbone are the heart, spleen, stomach, pancreas, and large intestine. When you experience pain under the left breast, it can have a variety of causes — some simple, some serious. Because the heart is located left and center in the chest — and because heart disease is the leading cause of death in America — a heart attack is often the first thing people think of when they experience pain near their left breastbone. When there is pain, it can last for a few minutes or come and go. Learn more about the warning signs of a heart attack.