The heart is part of the cardiovascular system, also called the circulatory system. These two terms refer to the same thing: a network made up of the heart, blood, and blood vessels that delivers oxygen and nutrients to every cell in your body and carries waste products away.
What the Cardiovascular System Includes
The cardiovascular system has three main components: the heart, which acts as a muscular pump; a closed network of blood vessels (arteries, veins, and capillaries); and the blood itself. Together, these parts form a continuous loop that begins and ends at the heart.
Arteries are strong, muscular vessels that carry oxygen-rich blood away from the heart to the rest of the body. The largest and most important artery is the aorta, which exits the heart and branches into smaller arteries reaching every region of your body. Veins do the opposite, carrying oxygen-poor blood back toward the heart. The two largest veins, the superior and inferior vena cava, collect blood from the upper and lower body respectively and return it to the heart’s right side.
Capillaries are the smallest blood vessels, and they’re where the real work happens. These thin-walled vessels connect arteries to veins and act as transfer stations. Oxygen and nutrients pass through capillary walls into surrounding tissues, while carbon dioxide and other waste products move in the opposite direction. Thousands of miles of capillaries permeate every tissue in the body, reaching virtually every cell.
What the Heart Actually Does
The heart contains four muscular chambers that briefly hold blood before moving it along. The right side of the heart handles oxygen-poor blood, while the left side handles oxygen-rich blood. These two sides work simultaneously but serve different circuits.
Blood returning from the body enters the right atrium through the two large veins (the vena cava). From there it moves into the right ventricle, which pumps it to the lungs through the pulmonary artery. In the lungs, the blood drops off carbon dioxide and picks up a fresh supply of oxygen. This newly oxygenated blood then flows back to the heart’s left atrium via the pulmonary veins, passes into the left ventricle, and gets pumped out through the aorta to supply the entire body. Then the cycle repeats.
A healthy adult heart beats 60 to 100 times per minute at rest, though this varies by age. Newborns have much faster resting rates, typically 100 to 205 beats per minute, which gradually slow through childhood. By adolescence, the range settles into the same 60 to 100 range seen in adults.
How It Works With the Respiratory System
The cardiovascular system can’t do its job alone. It depends heavily on the respiratory system to reload blood with oxygen. Inside the lungs, the pulmonary artery delivers carbon dioxide-rich blood to tiny capillaries that surround air sacs called alveoli. Carbon dioxide moves from the blood into the air inside these sacs (to be exhaled), while oxygen moves from the inhaled air into the blood. This gas exchange is what keeps your tissues alive and functioning.
The circulatory system then carries that freshly oxygenated blood from the lungs to tissues and organs throughout the body, while simultaneously collecting carbon dioxide and metabolic waste for removal. It’s a continuous loop: the heart pumps, the lungs refresh the blood, and the vessels distribute it.
Signs of a Healthy Cardiovascular System
Blood pressure is one of the most common measures of cardiovascular health. According to 2025 guidelines from the American Heart Association, normal blood pressure is below 120/80 mmHg. Elevated blood pressure falls between 120 and 129 systolic (the top number) with the bottom number still under 80. Stage 1 hypertension starts at 130/80, and stage 2 hypertension begins at 140/90 or higher.
Resting heart rate is another useful indicator. A rate consistently above 100 beats per minute at rest (in adults) or significantly below 60 without an obvious explanation like regular athletic training can signal that the cardiovascular system isn’t working as efficiently as it should. Both blood pressure and resting heart rate are easy to check at home with inexpensive monitors, making them practical ways to keep tabs on the system your heart belongs to.