A contraction of the heart that pumps blood to the lungs and the rest of the body. The different parts of the heart contract in a precise sequence that is brought about by electrical impulses that emanate from the sinoatrial node at the top of the right atrium. Three phases make up a cycle of 1 heartbeat: the diastole (resting phase), the atrial systole (atrial contraction), and the ventricular systole (ventricular contraction). The rate at which contractions occur is called the heart-rate. The term pulse refers to the character and rate of the heartbeat when it is felt at certain points around the body (at the wrist, for example).
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