- Shortness of breath, breathlessness, is one of the most common reasons people see a cardiologist, and one of the most diagnostically important symptoms in cardiovascular medicine.
- The heart and lungs work as a unit. When the heart is not pumping efficiently, fluid backs up into the lungs, producing breathlessness that is often the first signal something is wrong.
- Breathlessness on exertion that is new, progressive, or out of proportion to effort deserves cardiac assessment, even if it seems to have an obvious non-cardiac explanation.
- A normal BNP blood test and a normal echocardiogram together substantially reduce the likelihood of a cardiac cause and redirect the investigation efficiently.
- Breathlessness at rest, particularly when lying flat, waking you from sleep, or accompanied by chest discomfort, requires prompt assessment, not a wait-and-see approach.
Breathlessness is such a common human experience, after exercise, after a shock, at altitude, that it is easy to normalise it when it shouldn’t be. Patients often come to me having been breathless for months, having attributed it to being unfit, getting older, putting on weight, or stress.
Sometimes those explanations are correct. But breathlessness is also one of the most important cardiac symptoms there is, and one of the most frequently under-investigated. The heart and lungs are inseparable in their function, and when the heart begins to struggle, the lungs are often the first place it shows.
Understanding what cardiac breathlessness feels like, what causes it, and when to seek assessment is genuinely important, because the earlier a cardiac cause is identified, the better the options for treatment.
Why the Heart Causes Breathlessness
The heart-lung connection
The left side of the heart receives oxygenated blood from the lungs and pumps it out to the body. When the left ventricle is not pumping efficiently, whether from heart failure, a weak muscle, a valve problem, or elevated pressures, blood backs up through the pulmonary circulation. Fluid accumulates in the lung tissue itself, making the lungs stiffer and gas exchange less efficient.
The result is breathlessness, the sensation of not being able to get enough air in, of breathing being harder than it should be. At rest this may be subtle or absent. With exertion, when the heart needs to increase its output and cannot do so adequately, the breathlessness becomes apparent.
Why it so often gets missed
The insidious onset of cardiac breathlessness is part of why it gets missed. It rarely arrives suddenly, it creeps in gradually, week by week. A person who used to walk briskly up a hill now walks slowly. Someone who carried groceries up the stairs now takes two trips. The brain unconsciously recalibrates what feels normal, and by the time the breathlessness is significant enough to seek medical attention, a meaningful period of cardiac stress may have already accumulated.
One of the most telling questions I ask in clinic is: “What could you do six months ago that you can’t do now?” That question unlocks the real story, because patients adapt so well to progressive breathlessness that they often don’t realise how much their functional capacity has changed until someone asks directly.
Cardiac Causes of Breathlessness
Heart failure
Heart failure, reduced pump function of the left ventricle, often expressed as a reduced ejection fraction, is the most common cardiac cause of breathlessness. The failing heart cannot maintain adequate output, pressures rise in the pulmonary circulation, and fluid accumulates in the lungs. Breathlessness on exertion is the hallmark symptom, often accompanied by fatigue, ankle swelling, and reduced exercise tolerance.
Heart failure with preserved ejection fraction (HFpEF), where the pumping function appears normal but the heart muscle is stiff and fills abnormally, is increasingly recognised and produces breathlessness through a subtly different mechanism, but the symptom pattern is similar.
Valve disease
Significant valve disease, particularly aortic stenosis and mitral regurgitation, can produce breathlessness as the heart compensates for abnormal flow across the valve. Aortic stenosis in particular can progress for years without symptoms, then produce breathlessness, chest pain, or fainting as the valve area becomes critically narrow. An echocardiogram identifies valve problems with precision.
Atrial fibrillation
AF causes breathlessness in two ways. The irregular rhythm and often elevated heart rate reduce the efficiency of cardiac filling and output, particularly in people whose hearts rely on the atrial contraction component that AF abolishes. Additionally, AF is often a manifestation of underlying cardiac disease that itself causes breathlessness. Many people first notice their AF through unexplained breathlessness rather than palpitations.
Coronary artery disease
Significant narrowings in the coronary arteries can cause breathlessness as an anginal equivalent, particularly in women, in people with diabetes, and in older adults, where classic chest pain may be absent or minimal. Breathlessness on exertion that resolves with rest, in someone with cardiovascular risk factors, should always raise the possibility of ischaemia.
Pulmonary hypertension
Elevated pressure in the pulmonary circulation, whether from left heart disease, lung disease, or primary pulmonary arterial hypertension, causes breathlessness that can be severe and progressive. It is a diagnosis that requires specialist assessment but is important not to miss, particularly in younger patients with breathlessness that seems disproportionate to their apparent health.
Non-Cardiac Causes, Important to Distinguish
Not all breathlessness is cardiac, and part of the clinical task is efficiently distinguishing between causes. The most common non-cardiac causes include asthma and COPD, pulmonary embolism (blood clot in the lungs), anaemia, obesity, deconditioning, anxiety and panic disorders, and thyroid disease.
Several of these can coexist with cardiac disease, which is why the investigation is rarely a matter of ruling out one thing, it is a matter of understanding which factor is the dominant contributor.
Heart failure
Fluid backs up into the lungs as the heart struggles to maintain output. Progressive exertional breathlessness is the hallmark.
Valve disease
Aortic stenosis and mitral regurgitation both produce breathlessness as the heart compensates for abnormal valve function.
Atrial fibrillation
AF reduces cardiac efficiency and output. Many people first notice AF through breathlessness rather than palpitations.
Coronary artery disease
Breathlessness on exertion as an anginal equivalent, particularly in women, older adults, and people with diabetes where chest pain may be absent.
Pulmonary hypertension
Elevated pressure in the pulmonary circulation, causes breathlessness that can be progressive and severe. Important not to miss in younger patients.
Non-cardiac causes
Asthma, COPD, pulmonary embolism, anaemia, deconditioning, anxiety, and thyroid disease, all require consideration and may coexist with cardiac causes.
Warning Patterns, When to Act Promptly
Not all breathlessness requires the same urgency. But certain patterns warrant prompt assessment rather than a routine appointment.
| Pattern | What it may suggest | Action |
|---|---|---|
| Breathlessness at rest or with minimal activity | Decompensated heart failure, pulmonary embolism, acute cardiac event | Same-day medical assessment |
| Waking at night breathless, needing to sit up | Paroxysmal nocturnal dyspnoea, a hallmark of heart failure | Prompt cardiac assessment |
| Breathlessness lying flat, needing extra pillows | Orthopnoea, fluid redistribution in heart failure | Prompt cardiac assessment |
| Sudden severe breathlessness with chest pain | Acute pulmonary oedema, pulmonary embolism, aortic dissection | Emergency services immediately |
| Progressive exertional breathlessness over weeks to months | Heart failure, valve disease, coronary disease, anaemia | Medical review within days |
| Breathlessness with palpitations | AF or other arrhythmia reducing cardiac output | ECG and medical review |
How Breathlessness Is Investigated
The first steps
The initial assessment of breathlessness combines a clinical history, what brings it on, how long it has been present, whether it wakes you at night, what makes it better or worse, with a physical examination and targeted investigations.
A 12-lead ECG provides immediate information about heart rhythm, rate, and any electrical evidence of heart disease. Blood tests, including BNP or NT-proBNP, full blood count for anaemia, thyroid function, and kidney function, provide important baseline information. A chest X-ray can show pulmonary congestion, cardiomegaly, or lung pathology.
The echocardiogram, the key cardiac test
An echocardiogram is the most informative single cardiac investigation for breathlessness. It assesses left ventricular function and ejection fraction, valve structure and function, chamber dimensions, and filling pressures. A normal echocardiogram makes a primary cardiac cause of breathlessness significantly less likely and redirects investigation efficiently.
BNP and NT-proBNP, the cardiac stress markers
Elevated BNP or NT-proBNP in someone with breathlessness strongly supports a cardiac cause and typically leads directly to echocardiography. A normal level in someone with breathlessness is genuinely reassuring, it makes significant heart failure unlikely. We have a dedicated article on BNP in the Diagnostic Tests section.
Further investigation
Depending on the findings, further investigation may include a CT coronary angiogram or stress test to assess for coronary disease, pulmonary function tests to assess for lung disease, CT pulmonary angiography for pulmonary embolism, or right heart catheterisation for pulmonary hypertension assessment.
Treatment Depends on the Cause
Breathlessness is a symptom, not a diagnosis, and its treatment follows directly from identifying and treating the underlying cause. Heart failure responds to the quadruple therapy regimen. Valve disease may require intervention when it reaches the threshold for repair or replacement. AF is treated with rate control, rhythm control, and anticoagulation. Coronary disease is managed with medication, stenting, or surgery depending on the anatomy and severity.
The most important step in every case is getting to the correct diagnosis, because treating breathlessness symptomatically without understanding its cause is never the right approach in cardiology.
- Is my breathlessness likely to be cardiac, and what investigations will confirm or exclude this?
- Should I have a BNP blood test and an echocardiogram as a starting point?
- How do I distinguish cardiac breathlessness from breathlessness due to lung disease, anaemia, or deconditioning?
- My breathlessness is worse lying flat / waking me at night, does that change the urgency?
- What functional changes should I watch for that would suggest my breathlessness is worsening?
Free Download, Heart Matters
Our Heart Health Risk Factor Checklist covers 12 cardiovascular risk categories, a useful tool to complete before any appointment investigating breathlessness, to ensure no relevant risk factors are overlooked.
Heart Matters Resource
When in Doubt, Get Checked Out
Breathlessness that is new, progressive, or out of proportion to your level of exertion deserves assessment, not reassurance without investigation. A BNP test and echocardiogram can answer the cardiac question quickly and efficiently.
Conclusion
Breathlessness is easy to explain away, and easy to under-investigate. The gradual adaptation that most people make to slowly worsening breathlessness means that by the time they seek help, a meaningful period of cardiac stress may already have passed.
The cardiac causes of breathlessness are well understood, well investigated, and well treated. An echocardiogram and a BNP test together answer the cardiac question quickly and redirect the investigation if the answer is non-cardiac. Neither test is invasive, neither takes long, and together they provide the most important diagnostic information available.
If you have been breathless in ways that feel new or different, and particularly if it is changing what you can and cannot do, that is the conversation worth having with your doctor sooner rather than later.
