Library · Physiology
Cardiac cycle
Make it clearer
The cardiac cycle is the sequence that repeats with every beat. What drives it is not a stray muscular shove but an ordered series of pressure changes inside the heart. Pressure is in charge: blood moves only when there is more on one side than the other.
Those pressure changes are produced by the myocardium, the heart muscle, and the myocardium contracts because an electrical signal reaches it. The signal starts in the sinoatrial node, the natural pacemaker, and makes the atria, the upper chambers, contract together. The signal then pauses for an instant at the atrioventricular node, and only then do the ventricles, the lower chambers, contract.
The valves are the doors that decide where the blood goes. They open and close on their own according to the pressure on each side, and as they close they produce the first and second heart sounds, the two you hear through a stethoscope.
In brief
The cardiac cycle is the series of pressure changes inside the heart that move blood from one chamber to the next.
Pressure is in charge: blood moves only when there is more on one side than the other.
Those changes arise from electrical conduction in the myocardium: the sinoatrial node makes the atria contract and then, after the pause at the atrioventricular node, the ventricles.
The valves direct that flow; their closure produces the first and second heart sounds.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Cardiac Cycle, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated