What is high blood pressure?
High blood pressure, also known as hypertension, is when the force of blood pushing against the walls of your arteries is consistently too high. It is measured using two numbers: systolic pressure, the force when your heart beats, over diastolic pressure, the force when your heart rests between beats. In the UK, high blood pressure is generally defined as a reading of 140/90 mmHg or higher when measured in a clinic, or an average of 135/85 mmHg or higher when measured at home, while an ideal reading sits between 90/60 mmHg and 120/80 mmHg. Only one of the two numbers needs to be raised for blood pressure to be considered high.
The reason high blood pressure matters so much is that it almost never causes symptoms, yet it quietly damages your arteries and forces your heart to work harder, steadily raising your risk of heart attack, stroke, kidney disease, and heart failure. This is why it is often called the silent killer. The reassuring part is that once it is identified, high blood pressure is very manageable through lifestyle changes and, where needed, medication. In our experience, the hardest part is usually detection rather than treatment, because so many people feel completely well while their blood pressure is doing harm in the background. The British Heart Foundation's information on high blood pressure is a useful companion to this guide.
What Do the Two Blood Pressure Numbers Mean?
A blood pressure reading is always given as one number over another, such as 120/80 mmHg. The top number, systolic pressure, is the pressure in your arteries at the moment your heart contracts and pushes blood out. The bottom number, diastolic pressure, is the pressure when your heart relaxes and refills between beats. Both matter, and in adults over 50 the systolic figure is generally the more important predictor of risk.
The unit "mmHg" stands for millimetres of mercury, the traditional way pressure has been measured in medicine. A healthy reading means your heart and arteries are under less strain, and your long-term risk of cardiovascular disease is lower.
What Counts as High Blood Pressure?
The NHS guidance on high blood pressure and NICE guidelines set out clear thresholds:
Ideal: below 120/80 mmHg
At risk (elevated): between 120/80 mmHg and 140/90 mmHg, a signal to take lifestyle measures seriously
Stage 1 hypertension: 140/90 mmHg or higher in clinic, or 135/85 mmHg or higher at home
Stage 2 hypertension: 160/100 mmHg or higher in clinic
Severe (stage 3): systolic over 180 mmHg or diastolic over 120 mmHg
A reading of 180/120 mmHg or higher, especially with symptoms such as chest pain, severe headache, or vision changes, is a hypertensive crisis and needs an emergency 999 call. For most adults, a single high reading does not confirm hypertension, which is diagnosed from a consistent pattern over time.
What Causes High Blood Pressure?
There are two broad types. Primary (or essential) hypertension accounts for the large majority of cases and has no single identifiable cause, developing gradually over years as a result of ageing and lifestyle. Secondary hypertension is less common and is caused by another condition, such as kidney disease, hormonal disorders, sleep apnoea, or certain medications.
The main risk factors include age, a family history of high blood pressure, being of Black African, Caribbean, or South Asian descent, being overweight, eating too much salt, drinking too much alcohol, physical inactivity, smoking, chronic stress, and poor sleep. Many of these overlap with the risk factors for high cholesterol, which is why the two so often occur together.
Why High Blood Pressure Is So Dangerous
The danger of high blood pressure lies in the cumulative damage it does to your arteries. Constant excess pressure injures the artery walls, which accelerates the build-up of fatty plaque, a process explained in our guide to plaque build-up in the heart. Over years, this raises the risk of a number of serious conditions:
Heart failure, as the heart tires from working against high pressure
Kidney disease and damage to the small vessels in the eyes
Because this damage happens silently and gradually, high blood pressure is frequently only discovered once it has already contributed to one of these problems, which is exactly why routine checks are so valuable.
Does High Blood Pressure Have Symptoms?
For the vast majority of people, high blood pressure produces no symptoms at all, which is the single most important thing to understand about it. You cannot feel high blood pressure, and you cannot rely on how you feel to judge it. Occasionally, very high blood pressure can cause headaches, nosebleeds, or vision problems, but these are the exception rather than the rule. The only reliable way to know your blood pressure is to have it measured, which is why anyone unsure of their numbers should consider when to get a heart check.
How High Blood Pressure Is Diagnosed
Diagnosis is based on a consistent pattern of readings rather than one measurement. When a clinic reading is elevated, current NICE guidance recommends confirming the diagnosis with 24-hour ambulatory blood pressure monitoring, which records your blood pressure automatically across a full day and night as you go about normal life.
In our experience, a 24-hour ambulatory blood pressure monitor works better than one-off clinic readings for diagnosing hypertension because it captures your blood pressure across an entire day and night, filters out the white-coat effect, and shows whether your pressure genuinely stays high when you are relaxed and asleep. This distinction matters enormously, because treating someone who does not need it, or missing someone who does, both have real consequences.
How High Blood Pressure Is Treated
Treatment begins with lifestyle. Reducing salt intake, losing excess weight, exercising regularly, cutting back on alcohol, stopping smoking, and following a healthy diet can all lower blood pressure meaningfully, sometimes enough to avoid medication altogether. Where lifestyle measures are not enough, several effective medications are available, including ACE inhibitors, angiotensin receptor blockers, calcium channel blockers, and diuretics, often used in combination. The aim is to bring blood pressure into a safe range and keep it there long term.
How We Assess Blood Pressure at Heartsure
Across more than a decade of running diagnostic cardiology in Kingston-upon-Thames, we have completed in excess of 12,000 cardiac investigations, and blood pressure assessment is one of the most common and important parts of that work. A full evaluation through our diagnostic service can combine 24-hour monitoring with a consultation, blood tests to check kidney function and cholesterol, and where appropriate an ECG or echocardiogram to assess whether high blood pressure has already affected the heart.
We've found that a significant minority of patients sent to us with high clinic readings, often around a quarter, turn out to have normal blood pressure once we fit a 24-hour monitor, a pattern known as white-coat hypertension. Identifying this spares people unnecessary lifelong medication, while for those whose blood pressure truly is high, the same monitoring confirms it beyond doubt and guides the right treatment.
Conclusion
High blood pressure is a common, silent condition in which the pressure in your arteries is consistently too high, defined in the UK as 140/90 mmHg or above in clinic. Because it rarely causes symptoms yet steadily raises the risk of heart attack, stroke, and other serious conditions, knowing your numbers is one of the most valuable things you can do for your long-term health. The encouraging reality is that high blood pressure responds very well to lifestyle change and, where needed, medication, particularly when caught early.
If you would like your blood pressure assessed properly, you can contact Heartsure on 0208 255 5999, email info@heartsure.co.uk, get in touch through our contact page, or book an appointment online. Our team in Kingston-upon-Thames offers same-day appointments where clinically appropriate, and most patients are seen within the same week as their first enquiry.
