Why does stress cause palpitations?

When you're stressed, it initiates your body's fight or flight reaction, which is when you're preparing to do battle or run away from somebody. This pumps out loads of adrenaline, which causes your blood vessels and your heart to react. In order to get more blood to the rest of the body, the heart increases how hard it pumps and how fast it pumps, and what people are talking about when they say 'palpitation' is the feeling of your heart beating abnormally fast or hard. So it's all down to adrenaline, and it's also what causes panic attacks.