The pumping action of the heart circulates the blood throughout the body and a sequence of events, jointly called the cardiac cycle, make this pumping action posible. Generally, the cardiac cycle can be divided into two separate periods: the contraction of the heart muscles, called systole, and the relaxation period, known as diastole. Systole and diastole occur through a series of events marked by structural changes of the cardiac chambers, the atria and ventricles.
Ventricular Filling
During relaxation of the heart muscles, or diastole, blood fills the atria and passes through the open valves, or flap-like structures in-between the atria and ventricles that prevent back flow, to fill the relaxed ventricles. According to CliffsNotes.com, ventricular filling consists of three successive events, including rapid filling followed by a slower filling, called diastasis, due to the already occupied volume. Ventricular filling ends with the remaining small volume of blood in the atria being forced into the ventricles concurrently with the next cardiac cycle event–atrial contraction.
Atrial Contraction
As ventricular filling comes to an end, contraction of the atria marks the beginning of systole. The sino-atrial node (SA node), also known as the heart’s pacemaker, sends electrical signals that cause the atria to contract, ejecting the remaining volume of blood within the atria into the ventricles and closing the valves to prevent back flow, according to the Texas Heart Institute. The two valves dividing the four chambers of the heart are the mitral and tricuspid valves.
Ventricular Contraction
The electrical signals from the SA node travel through the intrinsic conduction system of the heart and carry along the waves of contraction towards the ventricles. Pressure increases as the ventricular walls contract, forcing the pulmonary and aortic valves to open and the blood to eject out of the heart towards the lung from the right ventricle and towards the rest of the body from the left ventricle. As the contraction tapers off, the heart returns to a relaxed state and the cardiac cycle repeats again.
About this Author
Based in Chicago, Jojo Genden is passionate about sharing her health and wellness expertise through writing since 2008. She holds a Bachelor of Science in biology from Rockford College, and a Bachelor of Science in nursing from Edinboro University of Pennsylvania. Genden is a registered nurse in the state of Illinois with a background in intensive care.
