What controls the heart rate?

The heart has a very well designed electrical system, which has it's own internal pacemaker that beats very regularly, a bit like a metronome. That metronome will speed up if the heart needs to beat faster, for example at times of exercise or stress. The heart will beat slower when we are relaxed, for example when we are resting or when we are asleep at night. The heart has a well regulated metronome, however there are some conditions where that metronome can become damaged or impaired. In these cases we can fit the person with a pacemaker, which is a small box that sits just underneath the person's collar bone and feeds wires inside the heart; taking over the heart's own pacemaker at times when it becomes impaired.