An electrocardiograph is a device for measuring electrical activity at the body surface. The electrical activity is generated by neuromuscular and cardiac tissue activity but, as the objective is to document cardiac muscle activity, precautions should be taken to minimize skeletal muscle movement. The electrocardiogram (ECG) produced is a record of the potential difference (in mV) between electrodes plotted on the vertical axis against time (in seconds) plotted on the horizontal axis. Electrical activity is generated in cardiac tissue by changes in the transmembrane electrical potentials as a result of ion movement. This electrical activity then triggers myocardial cell contraction and is therefore essential for normal cardiac function. In the heart, pacemaker cells are located in the sinoatrial (SA) node and also in the atrioventricular (AV) node, Bundle of His, bundle branches and Purkinje fibres. These pacemaker cells have the ability to depolarize spontaneously (automaticity). The SA node depolarizes spontaneously at the fastest rate and is therefore the dominant pacemaker under normal conditions. The rate of discharge of the SA node can be influenced by numerous external factors, primarily sympathetic and parasympathetic tone. Electrocardiography; and Ambulatory monitoring are discussed.