How the heart and lungs work together

Your heart and lungs are designed to work together every second of every day.

Together, they deliver oxygen to every cell in your body, remove carbon dioxide, and keep your organs functioning properly. Because they rely so heavily on each other, a problem affecting one often places extra strain on the other.

The heart and lungs together are known as the cardiopulmonary system.

Many people think of heart and lung diseases as completely separate conditions.

However, because the heart and lungs work together as one connected cardiopulmonary system, they are closely linked, meaning that symptoms can overlap and disease in one organ can increase the risk of developing disease in the other.

Some diseases affect both the heart and lungs from the outset, while others may originate in one organ but eventually place significant stress on the other.

Shared symptoms such as breathlessness, fatigue, and reduced exercise capacity often occur in both heart and lung diseases.

Chronic respiratory diseases are associated with an increased risk of cardiovascular conditions.

The right side of the heart pumps blood into the lungs, where oxygen is absorbed, and carbon dioxide is removed (pulmonary circulation).

If the lungs become diseased or damaged, pressure can build within the pulmonary circulation, forcing the heart to work harder. Over time, this can lead to failure of the right side of the heart.

Conversely, when the left side of the heart weakens or is damaged, blood can back up into the lungs.

Research increasingly shows that respiratory and cardiovascular diseases commonly occur together in the same patient, creating complex health challenges that require coordinated care.

Because the heart and lungs interact, symptoms may arise from problems affecting either organ or both simultaneously.

Common warning signs

• Shortness of breath
• Chest pain or tightness
• Unusual fatigue
• Chest discomfort
• Dizziness
• Swollen ankles
• Reduced ability to exercise
• Conditions that affect both the heart and lungs

Some heart-lung (cardiopulmonary) conditions affect both the heart and lungs from the beginning.

Others may start in one organ but eventually place significant strain on the other.

Symptoms are often shared between heart and lung disease, sometimes making diagnosis difficult.

The following conditions demonstrate the close relationship between the heart and lungs.

Although each condition develops differently, they all illustrate how closely these two organs depend on one another to maintain healthy circulation and oxygen delivery.

Pulmonary hypertension (PH) places strain on both the heart and the lungs.

It is high blood pressure in the lungs, affecting the arteries that carry blood from the right side of the heart to the lungs.

Unlike general high blood pressure (hypertension), which affects arteries throughout the body, pulmonary hypertension is confined to the pulmonary arteries.

The increased pressure in these arteries forces the heart to work harder to pump blood through the lungs, straining both systems.

Over time, this extra workload can weaken the heart and result in right-sided heart failure.

The strain on both systems (the heart and the lungs) results in the most common symptom, unexplained shortness of breath, especially during physical exertion.

It can be challenging to diagnose and treat because the symptoms, most commonly breathlessness, may be associated with other conditions, and patients may see multiple doctors before finally receiving a diagnosis.

Pulmonary hypertension is classified into five groups based on different causes, with Group 1 (pulmonary arterial hypertension) being rare and other groups, such as Group 2, caused by left heart disease, being more common.

Although Group 1 pulmonary hypertension remains a serious condition, treatment has advanced, and new medicines continue to improve quality of life and survival.

While there isn’t a cure for it, there are effective therapies and treatments that slow down the progression of the disease and treat the symptoms.

Several therapies routinely available in some overseas countries are not yet publicly funded in New Zealand.

One new drug in particular for Group 1, sotatercept (brand name Winrevair), has shown in recent clinical trials to significantly improve exercise capacity and reduce disease progression in selected patients with pulmonary arterial hypertension.

Pulmonary embolism shows the close connection between the heart and lungs.

It occurs when a blood clot, usually originating as a blood clot (deep vein thrombosis (DVT)) in the legs, travels through the bloodstream and blocks a pulmonary artery.

This sudden blockage increases strain on the right side of the heart and reduces oxygen levels in the body by preventing blood from getting to parts of the lung, with large emboli potentially being life-threatening.

Sarcoidosis is an inflammatory disease in which small clusters of immune cells (granulomas) form in the body's organs.

The lungs are affected in around 90% of people with sarcoidosis, but the disease can also involve the heart.

Cardiac sarcoidosis may disturb the heart's electrical system, causing abnormal heart rhythms, heart block, and in some cases heart failure, and it can occur alongside lung disease or on its own.

Because it can affect the lungs and heart simultaneously, sarcoidosis is a clear example of a condition that crosses the boundary between the two organs.

Environmental exposures, including cigarette smoke, air pollution, occupational dust, and other toxins, further contribute to cardiopulmonary diseases worldwide.

Long-term exposure to these environmental factors is now recognised as a major modifiable risk factor for conditions affecting both the heart and lungs.

As well as damaging the lungs as we breathe, fine particles in smoke or air pollution can harm the entire cardiovascular system, including the heart and blood vessels.

The World Health Organization estimates that around 4.2 million premature deaths globally in 2019 were due to fine particulate matter, which causes cardiovascular and respiratory diseases and cancer.

Many people believe vaping is simply inhaling harmless water vapour. However, research has shown that this is not the case.

Although e-cigarettes do not produce tobacco smoke, the aerosols they create contain a complex mixture of chemicals that may affect both the lungs (respiratory system) and the heart (cardiovascular system).

Alongside the primary agent, nicotine, e-cigarettes contain numerous harmful chemicals that have been associated with lung disease.

Most vaping liquids contain propylene glycol, vegetable glycerine, nicotine, flavouring agents, and other additives. When heated, these substances can generate potentially harmful chemicals, including aldehydes, ultrafine particles, and toxic by-products.

E-cigarette aerosols contain chemicals and tiny particles that may harm the heart and lungs.

A growing body of medical research confirms that vaping aerosols are not harmless “water vapour”. They contain a toxic mixture of chemicals, heavy metals, and ultrafine particles that are inhaled deep into the lungs and readily enter the bloodstream, potentially directly threatening both heart and lung health.

Research has shown that vaping is associated with increased oxidative stress, inflammation, endothelial dysfunction, and vascular injury, processes that contribute to cardiovascular disease.

Studies have also identified effects on blood vessel function, blood pressure regulation, and heart rhythm.

Many lung diseases don’t stay confined to the lungs. Reduced oxygen levels, chronic inflammation, and increased blood pressure inside the lungs can all place extra strain on the heart.

Chronic respiratory disease doesn’t just affect breathing; it also places extra stress on the heart. COPD is a progressive lung disease that includes chronic bronchitis and emphysema, and is usually caused by smoking.

Reduced oxygen levels and chronic inflammation place additional stress on the cardiovascular system.

People with COPD often have cardiovascular diseases; they are at increased risk of coronary artery disease, heart failure, heart rhythm abnormalities, and pulmonary hypertension.

Unfortunately, cardiovascular disease may be undiagnosed and untreated in patients with COPD because the symptoms are attributed to COPD.

It is important to assess cardiovascular diseases (CVD) in people with COPD, especially those who experience acute symptom episodes, so they can receive timely interventions for both diseases.

Cardiovascular disease is a major cause of illness and death among people living with COPD.

Cor pulmonale is right-sided heart failure caused by chronic lung disease.

Conditions such as chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, and severe sleep apnoea can increase pressure in the pulmonary circulation, eventually weakening the right ventricle of the heart.

Every lung infection causes inflammation.

Over many years, repeated inflammation doesn’t just damage the lungs; it may also affect the heart.

Both COPD and bronchiectasis are associated with an increased risk of cardiovascular disease.

The persistent inflammation associated with bronchiectasis can also affect the cardiovascular system, increasing the risk of heart disease over time.

Bronchiectasis is a chronic lung condition that causes the airways to thicken, leading to mucus build-up, recurrent infections, coughs and shortness of breath.

There is no cure, but bronchiectasis can be treated, and the main aim is to keep the lungs clear of excess mucus through pulmonary rehabilitation and infection management.

Increasing evidence indicates that bronchiectasis increases the risk of cardiovascular disease.

This association is probably driven by inflammation, oxidative stress, and the additional strain that recurrent pulmonary infections place on cardiac health.

Asthma is usually thought of as a disease of the airways, but it can also affect the heart.

The chronic inflammation of long-term (persistent) asthma is not always confined to the lungs.

In a large population study, adults with persistent asthma had a significantly higher risk of cardiovascular events, including heart attack and stroke, than people without asthma.

Keeping asthma well controlled may therefore help protect the heart as well as the lungs.

Sleep is essential for health; poor sleep caused by obstructive sleep apnoea (OSA) affects the heart.

Breathing interruptions during sleep repeatedly stress the heart, lowering oxygen levels and triggering stress responses.

Untreated OSA increases the risk of hypertension, atrial fibrillation, heart failure, coronary artery disease, stroke, and pulmonary hypertension.

Interstitial lung diseases (ILDs) are caused by inflammation and scarring of lung tissue.

Pulmonary fibrosis, one of the most severe forms, stiffens the lungs and impairs oxygen exchange. As oxygen levels decline, pulmonary artery pressures may rise, increasing the risk of pulmonary hypertension and right-sided heart failure.

Serious respiratory infections, including pneumonia, influenza, respiratory syncytial virus (RSV), and COVID-19, can have significant effects on the heart.

Inflammation triggered by infection may increase the risk of heart attacks, heart failure, myocarditis, and cardiac arrhythmias.

People with pre-existing cardiovascular disease are particularly vulnerable to complications during severe infections.

Lung cancer can directly affect the heart through tumour growth, inflammation, treatment side effects, and blood clot formation.

Patients may experience cardiovascular complications such as arrhythmias, pericardial disease, pulmonary embolism, and heart failure.

The relationship between cancer and cardiovascular disease has become an important area of medicine known as cardio-oncology.

The relationship between the heart and lungs works both ways. While lung diseases can place extra strain on the heart, heart disease can also significantly affect the lungs and breathing.

Heart disease can reduce the heart's ability to pump blood effectively, increase pressure in the blood vessels of the lungs, and cause fluid to build up within the lungs or around them.

Heart failure is a heart condition that directly affects the lungs.

Instead of flowing forward through the body, blood accumulates in the lungs’ blood vessels, increasing pressure and causing fluid to leak into the lung tissue. This makes it much harder for oxygen to enter the bloodstream.

Heart failure often develops because of other cardiovascular diseases.

One of the most common underlying causes is coronary artery disease.

Coronary artery disease occurs when the arteries supplying blood to the heart become narrowed or blocked.

It can weaken the heart muscle after a heart attack or repeated injury, which may eventually lead to heart failure and fluid accumulation in the lungs.

Problems with the heart’s valves can also affect the lungs by disrupting normal blood flow and increasing pressure within the heart.

Heart valve disease affects the valves that ensure blood flows in the correct direction through the heart.

When valves narrow or leak, pressures within the heart can rise and eventually affect the lungs.

Over time, this increased pressure is transmitted backwards into the pulmonary circulation, making it harder for blood to move efficiently through the lungs.

Abnormal heart rhythms can also reduce the heart’s ability to pump blood effectively.

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia.

Atrial fibrillation causes the heart to beat irregularly and often rapidly.

This reduces the heart's pumping efficiency.

Some people are born with structural heart problems (congenital heart disease) that alter the way blood flows between the heart and lungs.

If a heart defect allows too much blood to flow into the lungs over many years, the pulmonary arteries can become damaged, pressures rise, and severe pulmonary hypertension can develop, a complication known as Eisenmenger syndrome.

Thanks to modern surgery, most people born with heart defects now survive well into adulthood, but many need lifelong follow-up of both their heart and lung health.

Understanding the relationship between the heart and lungs is essential for preventing disease, recognising symptoms early, and improving outcomes.

As research continues to uncover the complex interactions between these two vital organs, integrated cardiopulmonary care will become increasingly important for improving health and quality of life for people in Aotearoa New Zealand.