Your heart works tirelessly, beating around 100,000 times a day to keep you alive. With every beat, it pumps blood filled with oxygen and nutrients to every part of your body. Yet most people never stop to think about what actually happens during each heartbeat. If you have recently undergone a cardiac evaluation or read your medical reports, you may have heard terms like ‘systole’, ‘diastole’ or ‘cardiac cycle’. Understanding these concepts can help you make sense of your heart function and feel more confident when discussing your care with a doctor.
This guide explains the cardiac cycle in clear, simple language while keeping the science accurate. By the end, you will understand how your heart works, what happens during a typical heartbeat and why disruptions in the cardiac cycle lead to symptoms like breathlessness, fatigue or irregular heartbeats.
This blog is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified cardiologist to discuss your individual condition, ICD-10 codes, and treatment options. If you experience new or worsening symptoms, seek medical attention promptly.
This blog has been medically reviewed by the cardiac team at Heart Valve Experts (HVE).
The cardiac cycle is the complete sequence of events that occurs during one heartbeat. It begins the moment your heart starts filling with blood and ends when it has pumped that blood out and prepares to fill again.
In medical terms, it has two major components:
To understand this better, imagine your heart as a four-chambered pump. The upper chambers are the atria, and the lower chambers are the ventricles. Each chamber has valves that open and close at precise moments. This careful coordination ensures blood always flows in the right direction.
When the cardiac cycle works smoothly, your organs receive the oxygen and nutrients they need. When it is disrupted, you may experience symptoms that signal an underlying heart problem.
If you place your hand on your chest, you feel your heart beating repeatedly. Each beat is one cardiac cycle. In simple terms, this is what happens during each cycle:
The right atrium receives deoxygenated (oxygen-poor) blood from the body. The left atrium receives oxygen-rich blood from the lungs.
The ventricles contract to push blood forward. The right ventricle sends blood to the lungs, and the left ventricle sends blood to the entire body.
The heart relaxes briefly so the chambers can refill.
At rest, this entire process takes about 0.8 seconds.
This pattern continues throughout your life, adjusting automatically when you exercise, sleep or feel stressed.
To understand the cardiac cycle properly, we break it into the two core phases:
The heart contracts to pump blood out. First the atria contract, then the ventricles contract with greater force.
The heart relaxes and fills with blood. This phase is essential because without proper filling, the next heartbeat cannot generate enough output.
Understanding systole and diastole helps you follow what happens in more detailed phases of the cardiac cycle.
Although the cycle happens quickly, medical science divides it into distinct phases. This helps identify where something may be going wrong if symptoms or abnormal test results appear.
1. Atrial Diastole
The heart is relaxed and filling with blood from the body and lungs.
2. Atrial Systole
The atria squeeze and push extra blood into the ventricles.
3. Isovolumetric Ventricular Contraction
The ventricles tighten, valves close, and pressure builds. No blood moves yet.
4. Ventricular Ejection
The ventricles pump blood out to the lungs and to the rest of the body.
5. Isovolumetric Ventricular Relaxation
The ventricles relax, pressure drops, and valves close again.
6. Rapid Filling
Blood flows quickly from the atria into the ventricles.
7. Reduced Filling (Diastasis)
Filling continues slowly as the heart prepares for the next beat.
Together, these seven phases repeat with every heartbeat to keep blood moving through your body and sustain life.
Understanding the cardiac cycle is more than an academic exercise. It helps explain why certain symptoms appear when something is wrong.
The cardiac cycle allows your body to:
If even one phase becomes disrupted, the entire process becomes inefficient. This is why conditions like valve disease or arrhythmias can quickly cause fatigue and breathlessness.
Many cardiac conditions alter how the heart fills, contracts or relaxes. A few common examples are:
If a valve becomes narrowed or leaks abnormally, the timing and flow of the cardiac cycle are disrupted, and that’s how heart valve disease develops.
For example:
If the electrical signals become irregular, the atria and ventricles contract out of sequence. This affects filling and pumping.
The heart may become weak and unable to pump effectively or stiff and unable to fill properly.
These disruptions help cardiologists understand why symptoms develop and how to plan the right treatment.
Common signs include:
If any of these occur, early evaluation is important because many cardiac conditions are more manageable when detected early.
Understanding the cardiac cycle shows how delicate and complex your heart function is. When even one part of the cycle becomes disrupted, specialised assessment is crucial.
Centres such as Heart Valve Experts (HVE) in Mumbai focus deeply on conditions that affect the cardiac cycle, including valve disease and heart failure. They use:
This expertise ensures every step of your heart function is evaluated with precision and treated with the safest, most advanced approach available.
The cardiac cycle is the fundamental sequence that keeps your heart beating and your body alive. It has two main phases, systole and diastole. Within these, several detailed steps ensure efficient filling, pumping and relaxation. When the cycle works properly, your organs receive oxygen and nutrients. When it is disrupted, symptoms such as breathlessness, murmur, fatigue or palpitations may appear.
Understanding the cardiac cycle helps you make sense of your symptoms, ECG reports and echocardiograms. It also explains why certain conditions need timely treatment.
If you ever have concerns about your heart rhythm, valve function or symptoms, choosing a specialised centre with experience in structural heart care can make a significant difference. Heart Valve Experts combine advanced technology with patient-centred care, helping you protect your heart health with clarity and confidence.
The cardiac cycle is the series of events in one heartbeat. It includes how the heart fills with blood, contracts, and relaxes. This answers what is cardiac cycle in the simplest way.
The cardiac cycle function is to pump blood effectively to the body. Understanding the cardiac cycle meaning helps explain how each heartbeat works.
Valve disease, arrhythmias, high blood pressure, heart failure, and coronary artery disease can affect the cardiac cycle phases and overall cardiac cycle steps.
Tests like ECG and echocardiography help assess the cardiac cycle of the heart. They show how the heart fills, contracts, and relaxes, similar to what you see in a cardiac cycle diagram or cardiac cycle flow chart.
Seek evaluation if you have symptoms that may indicate issues in the stages of cardiac cycle. A specialist can explain the cardiac cycle and check if any part is disrupted.
