An Electrocardiogram of the Heart is the recording of small electric waves being generated during heart activity. The term electrocardiograph is derived from three Greek words 'electro' meaning related to electrical activity, 'cardio' meaning heart, and 'graph' meaning to write. It is used worldwide as a simple way of diagnosing heart conditions.
Electrical activity of heart: In the heart there are specialized cells called pacemaker cells. When the heart muscle is at rest, the pacemaker cells are negatively charged and when the heart contracts they are positively charged. These cells produce small electrical signals b changing their electrical from positive to negative and back. The heart cells have the ability to spread its electrical charge to its adjacent cells. This initial trigger is enough to produce a chain reaction. Thus the electrical activity of heart starts at the top of the heart and spreads down. So this tiny electric shock spreads down to heart causing it to contract. The contraction of heart results in the pumping of blood.
For the cardiovascular system to work properly, the atria and ventricles must operate in proper time relationship. During each cycle of ECG, the action potential in the heart originates near the top of the right atrium at a point called the pace maker or sino-atrial node (SA node). Pacemakers are specialized cells that generate action potentials at a regular rate. It is necessary that to initiate the heart beat, the action potentials generated by the pacemakers propagate in all directions along the surface of atria. These propagating waves terminate at a point near the center of the heart called AV node (Atrio-ventricular node). As told earlier, the action of atria and ventricles must have a proper timing relationship. This is provided by some special fibers at the AV node. These fibers act as a delay line to provide the timing between the atria and ventricles. So after the electrical excitation passes through the delay line, it is spread rapidly to all parts of both ventricles by the bundle of His. Purkinje fibers are special fibers present in the bundle of His.
Usually heart problems can produce a wide range of symptoms. Without the help of ECG it may not be possible to tell whether the symptoms are caused by a heart problem. Symptoms are chest pain, shortness of breath, palpitations, abdominal pain, weakness etc. In some cases ECG reveals a problem that is not cardiac in nature. Ex: Overdose of certain drugs, electrolyte abnormalities etc.