Blood pressure and heart rate

Blood pressure is the most ordinary number in medicine and one of the most consequential. It is taken at almost every appointment, written as a tidy pair like 120/80, and then — for most of us — promptly forgotten. Yet raised blood pressure is, by the global numbers, the single largest preventable cause of death on the planet: it sits behind a huge share of heart attacks, strokes, kidney failure and dementia, and it does its damage silently, over decades, with no symptoms to warn you. Roughly a third of adults have it, and a large fraction of them don't know.

This page is for anyone who wants to actually understand that number from the inside out: what the two figures mean and where they come from, how the thresholds were chosen (and why the UK and US disagree on them), what high pressure does to your arteries and organs over time, the strange history of how we learned to measure it at all, and what the modern toolkit — lifestyle and drugs — can do about it. It is written to be useful whether your reading is perfect, borderline, high, or you are simply curious about the most-measured number in your body.

What blood pressure actually is

Your heart is a pump, and blood pressure is simply the force the blood pushes against the walls of your arteries as it travels round the loop. It is not constant: it rises and falls with every heartbeat, which is why a single reading is written as two numbers, not one. The cycle of one heartbeat has two phases, and each number captures one of them.

When the heart muscle contracts and ejects blood into the arteries, the pressure peaks. That peak is systolic pressure — the first, higher number. Then the heart relaxes and refills, the arteries recoil, and the pressure falls to a trough between beats. That trough is diastolic pressure — the second, lower number. So “120 over 80” means a peak of 120 and a trough of 80. The systole/diastole pair is the rhythm of the heart written as a fraction.

The unit, mmHg, is “millimetres of mercury”, and it is a fossil of how pressure was first measured: by how high the force could push a column of liquid mercury up a glass tube. A reading of 120 means the pressure would lift mercury 120 mm. We have long since replaced the mercury with electronic sensors, but the unit stuck, the way we still measure engine power in horsepower.

Pressure depends on two things: how hard the heart pumps (the volume of blood it pushes out per beat and per minute), and how much the arteries resist that flow. Resistance is the bigger lever in chronic high blood pressure — small arteries that are stiff or narrowed force the heart to push harder to move the same blood, and the pressure climbs. The body regulates all this constantly through the nervous system, the kidneys, and a cascade of hormones (the renin–angiotensin system), which is exactly the machinery most blood-pressure drugs target. The US National Heart, Lung, and Blood Institute has a good primer on this plumbing.

The numbers: categories and targets

There is no bright line where a healthy pressure suddenly becomes a dangerous one. Risk rises smoothly and continuously across the whole range — the higher the pressure, on average, the higher the long-term risk — so the categories below are useful conventions drawn across a slope, not natural cliffs. They exist to guide decisions, and reasonable experts (and countries) draw the lines in slightly different places.

A reading falls into the higher category if either number qualifies: 160/85 is treated on the strength of the 160.

Why the UK and US differ. In 2017 the American Heart Association and American College of Cardiology lowered the threshold for “hypertension” from 140/90 to 130/80, which at a stroke reclassified tens of millions of Americans. The UK’s NICE and the European Society of Cardiology have largely kept the diagnostic threshold at 140/90 in the clinic, while still encouraging treatment toward lower targets in higher-risk people. So the same person can be “hypertensive” in Boston and merely “high–normal” in Birmingham. The biology is identical; the disagreement is about where on the risk slope it is worth starting to act, and how to weigh the benefits of treating mild elevations against the costs and side-effects. The NHS sets out the UK numbers plainly.

One reading is not a diagnosis. Blood pressure swings minute to minute — with stress, caffeine, a full bladder, a brisk walk to the surgery, even the act of being measured. A single clinic reading is a snapshot of a moving target. Two distortions matter especially:

• White-coat hypertension — pressure that is high in the clinic, because the setting itself raises it, but normal at home. Treat the white coat as a reading, not a verdict.
• Masked hypertension — the opposite and more dangerous: normal in the clinic but genuinely high in daily life, so it goes undetected.

This is why modern guidelines lean on home monitoring and ambulatory monitoring — a wearable cuff that records automatically over 24 hours, including overnight — rather than a single clinic figure. Out-of-office readings predict risk better, and their thresholds are set a touch lower (a home average around 135/85 is roughly equivalent to 140/90 in the clinic) precisely because the white-coat effect is absent. Blood Pressure UK and the British Heart Foundation both explain how to read your own pressure properly.

Why it matters: what high pressure does

High blood pressure damages slowly, mechanically, and almost everywhere, because everywhere has arteries. Year after year, the extra force batters the delicate inner lining of the vessels, which thicken and stiffen in response. Stiff, narrowed arteries push the pressure higher still — a vicious cycle — and they ferry that excess force into whichever organ they feed.

The organs in the firing line:

• Arteries. Sustained pressure accelerates atherosclerosis — the build-up of fatty, fibrous plaques in artery walls — and stiffens the vessels. It also weakens them, which can balloon into an aneurysm that may burst.
• The heart. Pumping against high resistance forces the heart’s main chamber to thicken, like any over-worked muscle. That enlarged, stiffened heart is more prone to heart failure, to abnormal rhythms such as atrial fibrillation, and — via the diseased coronary arteries — to heart attack.
• The brain. Hypertension is the leading modifiable cause of stroke, both the clot kind (a blocked vessel) and the bleed kind (a burst one). It also quietly damages the brain’s tiny vessels over time, and is one of the strongest known risk factors for vascular dementia and a contributor to Alzheimer’s.
• The kidneys. The kidney is a dense filter of fine blood vessels, and high pressure scars them, degrading filtration. Worse, the kidneys help regulate blood pressure — so damage there pushes pressure higher, another vicious loop that can end in kidney failure.
• The eyes. The retina is the one place a doctor can actually see your small arteries directly. High pressure damages these vessels (hypertensive retinopathy), which can blur or threaten vision and which mirrors the unseen damage elsewhere.

The encouraging counterpart to all this is that the damage is largely preventable, and that even modest reductions pay off. Lowering systolic pressure by around 10 mmHg is associated, across large trials, with substantially fewer strokes, heart attacks and deaths. The CDC and the American Heart Association both frame blood-pressure control as one of the highest-leverage things in all of preventive medicine.

A short history of measuring it

For most of medical history blood pressure was invisible — you could feel a pulse, but not put a number on its force. The story of measuring it is a chain of clever, sometimes gruesome, improvisations.

The first true measurement was made on a horse. In 1733 the English clergyman and scientist Stephen Hales tied down a mare, opened an artery in her leg, and connected it to a tall glass tube. The blood rose more than eight feet up the tube and bobbed with each heartbeat — the first recorded blood-pressure reading, and a vivid, fatal demonstration that the blood was under real pressure. It was direct, quantitative, and utterly impractical for living patients.

Making it bloodless took another century and a half. In 1896 the Italian physician Scipione Riva-Rocci introduced the inflatable arm cuff — the sphygmomanometer in its recognisable modern form — which squeezed the artery shut and read off, on a mercury column, the pressure needed to stop the pulse. That gave the systolic number without spilling a drop of blood. The missing half arrived in 1905, when the Russian surgeon Nikolai Korotkoff placed a stethoscope below the cuff and listened: as he let the pressure down, he heard the blood begin to thump back through (systolic) and then fall silent as flow became smooth again (diastolic). Those Korotkoff sounds are what a clinician with a manual cuff is still listening for today.

Knowing the number did not yet mean knowing what it meant. Well into the twentieth century, raised pressure with no obvious cause was called “essential” hypertension — and “essential” carried the now-startling implication that the high pressure was necessary, a benign or even helpful adaptation to push blood through stiffening arteries. Eminent physicians warned against lowering it. US President Franklin Roosevelt’s blood pressure was allowed to climb into clearly dangerous territory in the 1940s and was treated as largely untreatable; he died of a massive brain haemorrhage.

The turn came with long-term population science. The Framingham Heart Study, begun in 1948 in a Massachusetts town and following its residents for decades, did more than any single project to prove that high blood pressure (along with cholesterol and smoking) was a genuine, measurable risk factor for heart disease and stroke — coining that very phrase. By the 1960s and 70s, controlled trials of the first effective drugs showed that lowering pressure cut strokes and deaths, demolishing the “benign” view for good. More recently the US SPRINT trial (2015) pushed in the other direction, finding that for many higher-risk patients an intensive target near 120 systolic beat the older 140 — one of the studies that nudged American guidelines lower and reopened the very debate about thresholds described above.

Current approaches: measuring, lifestyle, drugs

Measuring it well

Because so much rides on the number, getting it right matters more than people realise — a sloppy reading can over- or under-diagnose by a wide margin. The basics of a good measurement:

• Sit quietly for five minutes first; no caffeine, exercise or cigarette beforehand; empty your bladder.
• Sit with your back supported, feet flat on the floor, legs uncrossed.
• Rest the arm on a table so the cuff is at heart height, and use a correctly sized cuff — a too-small cuff reads falsely high.
• Don’t talk during the reading. Take two or three readings a minute apart and average them; a single high first reading is common and often settles.
• For diagnosis, readings over several days at home (or a 24-hour ambulatory monitor) beat one clinic figure.

Lifestyle: the first-line lever

For many people, especially those in the elevated and stage 1 ranges, lifestyle change alone can bring pressure down meaningfully — and it makes every drug work better on top. The evidence-backed moves:

• Salt. Cutting sodium is one of the most direct levers; much of the salt we eat is hidden in processed food, bread and restaurant meals rather than the salt cellar.
• The DASH diet (Dietary Approaches to Stop Hypertension) — rich in vegetables, fruit, whole grains, beans and low-fat dairy, light on red meat, sugar and salt — is one of the best-tested dietary patterns for lowering pressure.
• Exercise. Regular aerobic activity (brisk walking, cycling, swimming) reliably lowers pressure, and even isometric exercise like wall-sits shows benefit.
• Weight. Losing excess weight lowers pressure roughly in proportion — one of the most effective single changes for those carrying it.
• Alcohol. Heavy drinking raises blood pressure directly; cutting down lowers it. (See the companion guide to alcohol.)
• Sleep and stress. Untreated sleep apnoea is a common, reversible driver of resistant hypertension; chronic poor sleep and stress nudge pressure up too.
• Smoking. Each cigarette spikes pressure acutely, and smoking compounds every downstream cardiovascular risk. Stopping is among the highest-value health decisions there is.

The main drug classes

When lifestyle is not enough, a handful of well-understood, mostly cheap drug families do the work — often in low-dose combination, which controls pressure better with fewer side-effects than pushing one drug to its limit. The major classes:

UK guidance often starts younger patients on an ACE inhibitor or ARB, and older or Black African / Caribbean patients on a calcium-channel blocker, then combines as needed — the precise drug and order are a clinical decision, not a DIY one.

What the research says, and frontiers

Hypertension is, in one sense, a solved problem: we understand it, and we have safe, effective, inexpensive treatments. Yet it remains spectacularly under-controlled — across the world, only a minority of people with high blood pressure have it diagnosed, treated and brought to target. The gap is not mainly scientific; it is one of detection (no symptoms), persistence (lifelong daily pills for an invisible problem), access and adherence. Closing it would prevent more deaths than almost any new drug.

Where research is pushing:

• Renal denervation. A catheter procedure that quiets the nerves running to the kidneys — part of the pressure-regulating machinery. After early trials disappointed, refined techniques have shown modest but real benefit, and it is now an option for some people with stubborn, drug-resistant hypertension.
• The polypill. Combining several low-dose blood-pressure (and sometimes cholesterol) drugs in a single daily tablet improves adherence and control, and is being explored as a simple, cheap public-health tool, especially in lower-income settings.
• Longer-acting therapies. Trials of injectable treatments that lower pressure for months at a time aim squarely at the adherence problem — the difficulty of taking a daily pill for something you can’t feel.
• Ruling out secondary causes. Most hypertension is “primary” with no single cause, but a minority is secondary to something specific and fixable — kidney disease, sleep apnoea, thyroid problems, or hormone-secreting tumours such as in primary aldosteronism, which is more common than once thought. Spotting these can cure the high pressure outright.

Where to get help & more info

If you don’t know your blood pressure, getting it checked — at a GP surgery, a pharmacy, or with a validated home monitor — is one of the cheapest, highest-value things you can do for your long-term health. These are sound, authoritative starting points:

• NHS — High blood pressure (hypertension) — the plain UK overview, symptoms, diagnosis and treatment.
• Blood Pressure UK — a dedicated charity with practical guidance on measuring and lowering pressure.
• British Heart Foundation — broad, trustworthy heart-health information.
• WHO hypertension fact sheet — the global picture and the numbers.
• NHLBI (US NIH) and the American Heart Association — detailed US-oriented explainers.
• CDC — public-health data and prevention guidance.
• NICE — the UK clinical guidelines behind how doctors here diagnose and treat it.

Some of the figures and details on this page — typical ranges, statistics and the biology — were compiled with the help of AI tools and may contain errors or be out of date. They are shared in good faith for general interest only, and are not medical advice. Nothing here is a substitute for a doctor or a qualified health professional; if you are worried about your health, please seek professional help. Check claims against primary medical sources before relying on them.