Electrocardiogram (ECG, also known as an EKG) – a method of measuring the electrical activity of the heart. See the heart is the only organ that has its own, self-contained nervous system, beside the brain of course. This nervous system controls its rhythm. ECGs are usually written on a piece of paper by the machine being used to give such readings, usually these readings have several identifiable parts, which can be measured in size (i.e., their duration). One component is the QT interval, which, if prolonged, can lead to fatal cardiac arrest. Vasculature – blood vessels, such as arteries and veins.