The human heart is a muscular organ roughly the size of your fist. Its job is simple to describe and astonishing to sustain: pump blood — carrying oxygen and nutrients — to every tissue in the body, and carry waste products away, continuously, for an entire lifetime.
The four chambers
The heart has four chambers. The two upper chambers, the atria, receive incoming blood; the two lower chambers, the ventricles, pump it out with force. The right side handles oxygen-poor blood heading to the lungs; the left side handles oxygen-rich blood heading to the body. This "double pump" design keeps the two streams separate.
Valves keep blood moving one way
Four valves act as one-way doors between chambers and vessels, opening and closing with each beat to prevent backflow. The familiar "lub-dub" sound of the heartbeat is largely the sound of these valves closing.
The electrical system
Each heartbeat is triggered by a tiny electrical signal that begins in the sinoatrial node — the heart's natural pacemaker — in the right atrium. The signal spreads across the atria (making them contract), pauses briefly, then sweeps through the ventricles. This coordinated sequence is what an electrocardiogram (ECG) records.
The cardiac cycle
One full beat has two phases: systole, when the heart muscle contracts and pushes blood out, and diastole, when it relaxes and refills. At rest the cycle repeats roughly once per second, speeding up with exercise, excitement or stress and slowing during rest and sleep.
Keeping the pump healthy
Health authorities consistently emphasize the same foundations: regular physical activity, a balanced diet, not smoking, maintaining a healthy weight, and managing blood pressure and cholesterol. Warning signs such as chest pain, unusual breathlessness or fainting deserve prompt medical attention.
This article is for general information only and is not medical advice. If you have concerns about your heart, speak to a qualified healthcare professional.