Explain cardiac cycle stepwise?

The cardiac cycle refers to the sequence of events that occur during one complete heartbeat, involving the contraction (systole) and relaxation (diastole) of the heart chambers. The cardiac cycle consists of several steps, and I'll explain them step by step:

Atrial Contraction (Atrial Systole):

The cardiac cycle begins with the contraction of the two atria (upper chambers of the heart).
The contraction forces blood into the relaxed ventricles through the open atrioventricular (AV) valves (tricuspid valve on the right side and mitral valve on the left side).
This phase helps to complete the filling of the ventricles with blood before they contract.
Ventricular Filling (Early Diastole):

The atria relax, and blood continues to flow into them from the veins (e.g., superior and inferior vena cava, pulmonary veins).
As the ventricles relax after their previous contraction, the pressure within them drops below the pressure in the atria.
This pressure gradient opens the AV valves, allowing blood to flow from the atria into the ventricles.
Isovolumetric Contraction (Ventricular Systole - Isovolumetric Contraction):

The ventricles begin to contract, building pressure within them.
Initially, all heart valves are closed, so the ventricles are contracting against a closed system.
This phase is known as isovolumetric contraction because the volume of blood in the ventricles remains constant while pressure increases.
Ventricular Ejection (Ventricular Systole - Ejection):

The pressure in the ventricles surpasses the pressure in the major arteries (aorta on the left side and pulmonary artery on the right side).
The semilunar valves (aortic valve and pulmonary valve) open, allowing blood to be ejected from the ventricles into the respective arteries.
Blood flows into the aorta and pulmonary artery, and the ventricles continue to contract, pushing most of the blood out.
Isovolumetric Relaxation (Early Diastole):

After contraction, the ventricles start to relax.
The pressure in the ventricles drops rapidly, causing the semilunar valves to close and preventing backflow of blood into the ventricles.
All heart valves are closed during this phase.
Ventricular Relaxation (Late Diastole - Diastasis):

The ventricles continue to relax, and their pressure drops further.
The pressure in the atria increases as they continue to fill with blood.
The heart is in a state of relative relaxation during this phase, with both atria and ventricles in diastole.
The cardiac cycle then repeats, with the atria contracting again to push any remaining blood into the ventricles and restart the cycle.

It's important to note that the timing and duration of these phases can vary based on factors such as heart rate, exercise, and overall cardiovascular health. The coordinated events of the cardiac cycle ensure efficient pumping of blood throughout the body and maintain a continuous circulation of oxygenated and deoxygenated blood.