Pulse
A pulse (or heartbeat) is a throbbing of blood vessels as blood goes through them. You can feel someone's pulse in their wrist, thumb or neck, where vessels are closer to the skin. A normal pulse is below 100 beats per minute. Our pulse quickens when we exercise because the muscles being used need more oxygen. Unusually fast or slow or irregular pulse might mean sickness.
There are normally four heart sounds. Two of them, S1 and S2, can be heard with a stethoscope. Two other sounds, S3 and S4, can not be heard, but they can be seen using a machine called a phonocardiograph.
