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An Overview of The Cardiovascular and Blood Circulatory System

A patient-focused guide to An Overview of The Cardiovascular and Blood Circulatory System, with clinical context, evaluation considerations and supporting information.

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The cardiovascular system, also called the circulatory system, is the heart, the blood vessels and the blood they carry. The heart pumps blood; arteries carry it away from the heart, capillaries deliver it to the tissues, and veins return it to the heart.[1] Blood brings oxygen and nutrients to the cells and carries away carbon dioxide and other waste. The lungs are not part of the cardiovascular system itself, but one of its circuits, the pulmonary circulation, exists to carry blood through them so that it can pick up oxygen and release carbon dioxide.[2]

The Three Circulations

Blood travels in two main loops that meet at the heart. The coronary circulation, a branch of the systemic circulation, feeds the heart muscle itself.

Circulation Route What it does
Pulmonary Right ventricle, pulmonary trunk and arteries, lung capillaries, pulmonary veins, left atrium[2] Carries oxygen-poor blood to the lungs and brings oxygen-rich blood back to the heart; unlike systemic arteries, its arteries carry blood low in oxygen[1]
Systemic Left ventricle, aorta and its branches, capillaries throughout the body, veins, superior and inferior venae cavae, right atrium[2] Delivers oxygen-rich blood to virtually every tissue and returns oxygen-poor blood to the heart[2]
Coronary (a branch of the systemic circulation) Coronary arteries arising from the first part of the aorta, capillaries in the heart wall, cardiac veins draining through the coronary sinus into the right atrium[2] Supplies the heart muscle itself; when blood flow through it fails, heart muscle cells die, which is a heart attack (myocardial infarction)[2]

Exchange of gases and other substances happens between the blood in the capillaries, the smallest vessels, and the fluid around the cells. Arterioles feed the capillaries and venules collect from them.[1] The cells that line every vessel and control what crosses the vessel wall are described on our page on endothelial cells, and how new vessels grow is explained on our page on angiogenesis and vasculogenesis.

How Blood Moves Through the Four Chambers

The heart has four chambers. On each side there is an upper chamber, the atrium, which receives blood, and a lower chamber, the ventricle, which pumps it out. A wall called the interatrial septum separates the two atria, and the interventricular septum separates the two ventricles.[2] One complete pass of blood through the heart runs in this order:

  1. Oxygen-poor blood from the body enters the right atrium through the superior vena cava (from above the diaphragm) and the inferior vena cava (from below it); blood from the heart wall drains in through the coronary sinus.[2]
  2. It passes through the tricuspid valve into the right ventricle.[2]
  3. The right ventricle pumps it through the pulmonary valve into the pulmonary trunk and arteries, which take it to the lungs.[2]
  4. Oxygen-rich blood returns from the lungs through the pulmonary veins into the left atrium.[2]
  5. It passes through the mitral valve into the left ventricle.[2]
  6. The left ventricle pumps it through the aortic valve into the aorta and out to the body.[2]

The valves keep blood moving in one direction. The left ventricle has to generate much more pressure to push blood around the long systemic circuit, and its muscle wall is much thicker than that of the right ventricle.[2]

Facts About Our Cardiovascular System

  • Size and weight. A typical heart is about the size of a fist. It weighs about 250 to 300 grams in women and 300 to 350 grams in men.[2]
  • Heart rate. A normal resting heart rate in adults is 60 to 100 beats a minute.[3] At about 70 beats a minute, that is roughly 100,000 beats a day and close to 3 billion in an 80-year life.
  • Output. Each ventricle pumps on average about 5 litres a minute at rest, with a normal range of 4 to 8 litres; each beat ejects about 70 millilitres in a resting adult of 70 kilograms.[3] Five litres a minute is about 7,200 litres a day.
  • Burden of disease. Cardiovascular diseases are the leading cause of death worldwide: an estimated 19.8 million people died of them in 2022, 85% of them from heart attacks and strokes.[4]

Silent Heart Attacks and Symptoms in Women

A silent heart attack is one that is found later, usually on an electrocardiogram (ECG), without the person having been diagnosed at the time. In the US ARIC study of 9,498 adults without heart disease, silent heart attacks were found on routine ECGs over about nine years, and participants were then followed for deaths for about nine more years; silent heart attacks made up more than 45% of all new heart attacks. They were more common in men than in women, but in both sexes they were linked with a higher risk of later death from heart disease, and the increase in risk may be larger in women.[5]

Chest pain, pressure or tightness is the main symptom of a heart attack in women as in men. In the VIRGO study of 2,009 women and 976 men aged 18 to 55 years admitted with a heart attack, 87% of women and 89.5% of men had chest pain. Women more often had three or more other symptoms as well, such as pain in the jaw, neck, arms or between the shoulder blades, palpitations or upper abdominal discomfort. Women were more likely to put their symptoms down to stress or anxiety, and 53% of women who had seen a clinician about similar symptoms beforehand were told these were not heart-related, compared with 37% of men.[6] Women are also more likely than men to have shortness of breath, nausea, vomiting, and back or jaw pain.[4] An American Heart Association statement reviews these and other differences between women and men in how heart attacks present and are treated.[7] Most heart attacks cause discomfort in the centre or left side of the chest that lasts more than a few minutes, or goes away and comes back; it can feel like pressure, squeezing, fullness or pain. Other warning signs are pain or discomfort in the jaw, neck, back, arms or shoulders, shortness of breath, a cold sweat, and weakness or light-headedness, and women are more likely to have other symptoms such as unusual tiredness, nausea or vomiting.[8] These can occur with little or no chest pain: in the VIRGO study, women with an ST-elevation heart attack (STEMI, shown by a characteristic ECG change) were more likely than men to arrive without chest pain.[6] If you notice these symptoms in yourself or someone else, call your local emergency number straight away, even if you are not sure it is a heart attack, and even if the symptoms come and go. Do not drive yourself to hospital or let someone else drive you; an ambulance is the safest way to get there.[8][9]

Natural Strategies for a Healthy Heart

Cardiovascular disease covers conditions of the heart and blood vessels. Many involve narrowed or blocked arteries, which can lead to a heart attack or stroke. The most important behavioural risk factors are an unhealthy diet, physical inactivity, tobacco use and harmful use of alcohol.[4] High blood pressure, high cholesterol and smoking are key risk factors,[10] and in 2009 to 2010 about 47% of US adults had at least one of them uncontrolled.[11] Age, sex and family history also affect risk and cannot be changed.[10]

How to Improve Blood Circulation & Circulatory System Function

The American Heart Association’s dietary guidance focuses on the overall eating pattern rather than single foods or nutrients.[12] Its main points are to:

  • keep a healthy body weight by balancing the energy you eat and use;
  • eat plenty of fruits and vegetables, of many kinds, and choose whole grains;
  • choose healthy protein sources, mostly plants, with regular fish and seafood, low-fat or fat-free dairy, and, if you eat meat or poultry, lean and unprocessed cuts;
  • use liquid plant oils, such as olive oil, rather than tropical oils and partially hydrogenated fats;
  • choose minimally processed foods instead of ultra-processed ones, and keep added sugars and salt low;
  • if you do not drink alcohol, do not start; if you do, limit it.[12]

Regular exercise is the other main habit. In healthy volunteers, 30 minutes of moderate or intensive running raised the number of circulating endothelial progenitor cells in the blood to more than twice the resting level, with the peak 10 to 30 minutes after intensive running, while 10 minutes of running did not;[13] what this means for long-term heart health is still being studied. If you have heart disease, ask your doctor before starting a new exercise programme.

Where Cell Therapy Research Stands in Heart Disease

Stem and stromal cells have been tested in heart attack and heart failure for more than 20 years. The largest randomised trials have not met their main goals: in DREAM-HF, 565 people with heart failure received donor cells injected into the heart wall or a sham procedure, and repeat heart failure events were similar in both groups.[14] A Cochrane review of 38 smaller trials of bone marrow cells in chronic ischaemic heart disease and heart failure found a possible reduction in deaths but rated the evidence as low quality.[15] As of November 2026, no cell therapy for heart disease is on the US Food and Drug Administration list of approved cellular and gene therapy products.[16] In Japan, sheets of heart muscle cells made from donor induced pluripotent stem cells (RiHEART) received a conditional, time-limited approval for ischaemic cardiomyopathy on 6 March 2026; under this pathway, approval rests on safety and a reasonable prediction of benefit, and benefit has to be confirmed after marketing before full approval.[17] An earlier product conditionally approved in Japan in 2015, sheets made from the patient’s own skeletal muscle cells (HeartSheet), was refused full approval in July 2024.[18] The trials are set out in more detail on our angiogenesis page.

Published Clinical Citations

[1] ^ Betts JG, Young KA, Wise JA, et al. Anatomy and Physiology 2e, section 20.1: Structure and function of blood vessels. OpenStax, Rice University; 2022. https://openstax.org/books/anatomy-and-physiology-2e/pages/20-1-structure-and-function-of-blood-vessels

[2] ^ Betts JG, Young KA, Wise JA, et al. Anatomy and Physiology 2e, section 19.1: Heart anatomy. OpenStax, Rice University; 2022. https://openstax.org/books/anatomy-and-physiology-2e/pages/19-1-heart-anatomy

[3] ^ Betts JG, Young KA, Wise JA, et al. Anatomy and Physiology 2e, section 19.4: Cardiac physiology. OpenStax, Rice University; 2022. https://openstax.org/books/anatomy-and-physiology-2e/pages/19-4-cardiac-physiology

[4] ^ World Health Organization. Cardiovascular diseases (CVDs), fact sheet, 31 July 2025. https://www.who.int/news-room/fact-sheets/detail/cardiovascular-diseases-(cvds)

[5] ^ Zhang ZM, Rautaharju PM, Prineas RJ, et al. Race and Sex Differences in the Incidence and Prognostic Significance of Silent Myocardial Infarction in the Atherosclerosis Risk in Communities (ARIC) Study. Circulation. 2016;133(22):2141-8. https://doi.org/10.1161/CIRCULATIONAHA.115.021177

[6] ^ Lichtman JH, Leifheit EC, Safdar B, et al. Sex Differences in the Presentation and Perception of Symptoms Among Young Patients With Myocardial Infarction: Evidence from the VIRGO Study (Variation in Recovery: Role of Gender on Outcomes of Young AMI Patients). Circulation. 2018;137(8):781-790. https://doi.org/10.1161/CIRCULATIONAHA.117.031650

[7] ^ Mehta LS, Beckie TM, DeVon HA, et al. Acute Myocardial Infarction in Women: A Scientific Statement From the American Heart Association. Circulation. 2016;133(9):916-47. https://doi.org/10.1161/CIR.0000000000000351

[8] ^ US Centers for Disease Control and Prevention. About heart attack and symptoms. Page dated 24 October 2024. https://www.cdc.gov/heart-disease/about/heart-attack.html

[9] ^ National Heart, Lung, and Blood Institute. Heart attack: symptoms. Last updated 24 March 2022. https://www.nhlbi.nih.gov/health/heart-attack/symptoms

[10] ^ US Centers for Disease Control and Prevention. Heart disease risk factors. Page dated 2 December 2024. https://www.cdc.gov/heart-disease/risk-factors/index.html

[11] ^ Fryar CD, Chen TC, Li X. Prevalence of uncontrolled risk factors for cardiovascular disease: United States, 1999-2010. NCHS Data Brief No. 103. National Center for Health Statistics; August 2012. https://www.cdc.gov/nchs/products/databriefs/db103.htm

[12] ^ Lichtenstein AH, Appel LJ, Vadiveloo M, et al. 2021 Dietary Guidance to Improve Cardiovascular Health: A Scientific Statement From the American Heart Association. Circulation. 2021;144(23):e472-e487. https://doi.org/10.1161/CIR.0000000000001031

[13] ^ Laufs U, Urhausen A, Werner N, et al. Running exercise of different duration and intensity: effect on endothelial progenitor cells in healthy subjects. Eur J Cardiovasc Prev Rehabil. 2005;12(4):407-14. https://doi.org/10.1097/01.hjr.0000174823.87269.2e

[14] ^ Perin EC, Borow KM, Henry TD, et al. Randomized Trial of Targeted Transendocardial Mesenchymal Precursor Cell Therapy in Patients With Heart Failure. J Am Coll Cardiol. 2023;81(9):849-863. https://doi.org/10.1016/j.jacc.2022.11.061

[15] ^ Fisher SA, Doree C, Mathur A, et al. Stem cell therapy for chronic ischaemic heart disease and congestive heart failure. Cochrane Database Syst Rev. 2016;12(12):CD007888. https://doi.org/10.1002/14651858.CD007888.pub3

[16] ^ US Food and Drug Administration. Approved Cellular and Gene Therapy Products. Content current as of 30 October 2026. https://www.fda.gov/vaccines-blood-biologics/cellular-gene-therapy-products/approved-cellular-and-gene-therapy-products

[17] ^ Japan Agency for Medical Research and Development (AMED). Approval of RiHEART, iPS cell-derived cardiomyocyte transplantation therapy for ischemic cardiomyopathy. Last updated 23 March 2026. https://www.amed.go.jp/en/news/topics/20260220.html

[18] ^ Pharmaceuticals and Medical Devices Agency (PMDA). List of approved products: regenerative medical products. https://www.pmda.go.jp/english/review-services/reviews/approved-information/0004.html