Cardiovascular System

What the cardiovascular system is

The cardiovascular system (also called the circulatory system) is the body's internal transport network. It consists of the heart, a vast system of blood vessels (arteries, veins, and capillaries), and the blood that moves through them. Working together, these parts deliver oxygen and nutrients to every cell, carry away carbon dioxide and metabolic waste, distribute hormones and immune cells, and help regulate body temperature and fluid balance.

At its center is the heart, a muscular pump roughly the size of a fist. In an adult at rest it beats about 60–100 times per minute, and at a typical resting cardiac output of about 5 liters per minute it circulates the body's entire blood volume in roughly one minute. The blood vessels form a closed loop that, laid end to end, would stretch for thousands of miles, reaching nearly every tissue in the body.

How circulation works

Blood travels through the body in two connected circuits, both driven by the heart.

• Pulmonary circulation carries oxygen-poor blood from the heart to the lungs and back. Deoxygenated blood enters the heart through the superior and inferior vena cava, fills the right atrium, passes into the right ventricle, and is pumped through the pulmonary artery to the lungs, where it picks up oxygen and releases carbon dioxide.
• Systemic circulation carries oxygen-rich blood from the heart to the rest of the body. Freshly oxygenated blood returns through the pulmonary veins to the left atrium, moves into the left ventricle, and is forced out through the aorta to supply organs, muscles, and tissues.

One-way heart valves keep blood moving in the correct direction. The tricuspid and mitral valves sit between the atria and ventricles, while the pulmonary and aortic valves guard the exits to the lungs and body. The "lub-dub" of a heartbeat is the sound of these valves closing.

Gas and nutrient exchange happens in the capillaries — vessels so thin (a single cell layer) that oxygen, glucose, and waste can pass directly between blood and tissue.

Key organs and structures

• Heart: A four-chambered muscular pump. The left ventricle is the strongest chamber because it generates the high pressure needed to push blood through the entire body.
• Arteries: Thick, elastic vessels that carry blood away from the heart under high pressure. The aorta is the largest. Coronary arteries branch off the aorta to feed the heart muscle itself.
• Veins: Vessels that return blood to the heart, typically under lower pressure. Many contain one-way valves that prevent backflow, especially in the legs.
• Capillaries: Microscopic vessels where the actual exchange of oxygen, nutrients, and waste occurs.
• Blood: Carries red blood cells (oxygen), white blood cells (immunity), platelets (clotting), and plasma (fluid, proteins, hormones).

The heartbeat is coordinated by the heart's electrical conduction system, beginning at the sinoatrial (SA) node — the natural pacemaker — and is fine-tuned by the autonomic nervous system, hormones, and blood volume.

Common conditions

Cardiovascular disease is the leading cause of death in the United States. According to the CDC, about 919,032 people died from cardiovascular disease in 2023 — the equivalent of 1 in every 3 deaths — and one person dies from it about every 34 seconds.

• Coronary artery disease (CAD): The most common type of heart disease, caused by plaque buildup (atherosclerosis) narrowing the arteries that supply the heart. The CDC reports that about 1 in 20 adults age 20 and older (roughly 5%) have CAD.
• Heart attack (myocardial infarction): Occurs when blood flow to part of the heart is blocked. About 805,000 heart attacks happen in the U.S. each year, and about 1 in 5 are "silent" — causing damage without the person being aware of it.
• High blood pressure (hypertension): Often symptomless, it strains the heart and arteries over time. Under the 2017 ACC/AHA guideline, normal is below 120/80 mm Hg, and a reading of 130/80 mm Hg or higher is classified as hypertension (Stage 1).
• Stroke: Brain damage from interrupted blood flow, frequently linked to the same risk factors as heart disease.
• Heart failure, arrhythmias, and valve disease are other major conditions that affect the system's ability to pump effectively.

How to keep it healthy

Much cardiovascular disease is influenced by modifiable factors. The American Heart Association summarizes the essentials in "Life's Essential 8" — four behaviors and four health measures:

• Eat better: Emphasize vegetables, fruits, whole grains, lean protein, nuts, and non-tropical oils; limit sodium, added sugar, and processed foods.
• Be more active: Aim for at least 150 minutes of moderate or 75 minutes of vigorous activity per week.
• Avoid nicotine: Tobacco and vaping are leading preventable causes of death.
• Get healthy sleep: Consistent, adequate sleep supports heart health.
• Manage weight, blood lipids (cholesterol), blood glucose, and blood pressure — ideally tracked with a clinician.

These steps are associated with lower risk of heart attack, stroke, and other complications. This article is for general education and is not a substitute for personalized medical advice — talk with a qualified healthcare provider about your individual risk and before making changes to your health routine.

Sources

• [CDC — Heart Disease Facts](www.cdc.gov/heart-disease/data-research/facts-stats/index.html)
• [NHLBI/NIH — How the Heart Works: How Blood Flows Through the Heart](www.nhlbi.nih.gov/health/heart/blood-flow)
• [American Heart Association — Life's Essential 8](www.heart.org/en/healthy-living/healthy-lifestyle/lifes-essential-8)
• [2017 ACC/AHA High Blood Pressure Guideline](www.acc.org/Latest-in-Cardiology/ten-points-to-remember/2017/11/09/11/41/2017-Guideline-for-High-Blood-Pressure-in-Adults)
• [StatPearls (NIH/NCBI) — Physiology, Cardiovascular](www.ncbi.nlm.nih.gov/books/NBK493197)