As the body fluids and tissues are good conductors of electricity, the electrical activity within the heart can be detected by attaching electrodes to the surface of the body. The pattern of electrical activity may be displayed on an oscilloscope screen or traced on paper. The apparatus used is an electrocardiograph and the tracing is an electrocardiogram (ECG). The normal ECG tracing shows five waves which, by convention, have been named , S and T . The standard ECG originates from the SA node and is known as sinus rhythm. The rate of sinus rhythm is 60 to 100 beats per minute. A faster heart rate is called tachycardia and a slower heart rate, bradycardia. Acetylcholine is a neurotransmitter of parasympathetic system of nerves and slows down heart rate.

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