Hypertension is High Blood Pressure.
High blood pressure often causes no symptoms, or immediate problems, but it is a major risk factor for developing a serious cardiovascular disease (conditions that affect the functioning of the heart and the circulation of blood around the body), such as a stroke or heart disease.
High Blood Pressure Explained - NHS Choices
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High blood pressure has no symptoms, but if it's not treated it can damage the kidneys, heart and brain.