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  Introduction

The primary purpose of the cardiovascular system is to supply an adequate amount of blood to peripheral tissues to meet their metabolic demands at all times. The arterial system supplies tissues and organs throughout the body with oxygen, nutrients, hormones, and immunologic substances. Through venous return it removes wastes from tissues, routing deoxygenated blood through the lungs for excretion of metabolic wastes.

The heart is the size of a fist and as small as it is it carries an impressive workload over a lifetime. It beats 60 to 100 times per minutes without resting. The heart must be flexible and able to adjust to changes in the body's metabolic demands, often in a matter of seconds. Vigorous exercise can increase metabolic requirements of muscles as much as 20 times over their needs during rest. To meet these demands the heart accelerates it rate to increase cardiac output. Vessels must redistribute blood flow, shunting a greater proportion of blood to muscle tissues and away from internal organs.

The heart is unique and possesses several properties. It works as a pump by expanding and contracting without placing added stress on the cardiac muscle and without developing muscle fatigue. The heart pumps 4 to 8 liters per minute. This is equivalent to 6,000 liters per day. It has an inherent capability to generate electrical impulses that maintain proper rhythm regardless of other factors, such as heart rate, and ignores inappropriate electrical signals that might over stimulate the cardiac muscle.

The ECG is a valuable diagnostic tool for the healthcare provider whether they are a doctor, nurse, or specialist in cardiac rehabilitation. Understanding the ECG enables the healthcare provider to respond correctly and to treat dangerous and potential deadly arrhythmias as quickly and efficiently as possible. It is important to understand the mechanisms, cutting edge treatments and to know exactly what needs to be done to treat these deadly arrhythmias. New drugs and high tech equipment which can cardio-vert, defibrillate, and serve as a pace maker are constantly being evaluated and introduced into the healthcare system.