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Heart Anatomy & Physiology/Cardiac Cycle

How the Heart Pumps Blood: The Cardiac Cycle Explained

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Written by

Team, Swasth Hriday

Published on

December 30, 2024

Every second, your heart is busy pumping blood to every part of your body, making sure that oxygen and nutrients are delivered, and waste products are removed. But how exactly does this happen? How does the heart manage to pump blood efficiently without missing a beat? In this blog, we’ll dive into the cardiac cycle, the process through which the heart pumps blood, and explain how it all works in simple terms.

By understanding the cardiac cycle, you’ll gain a better appreciation of how your heart functions and why it’s so essential to your health. So let’s begin!

What Is the Cardiac Cycle?

The cardiac cycle is the process that happens every time your heart beats. It consists of two main phases—systole (when the heart contracts) and diastole (when the heart relaxes). Together, these phases allow the heart to fill with blood, pump it out, and ensure that fresh oxygen-rich blood is delivered to your organs while carbon dioxide-rich blood is sent to your lungs.

In a healthy adult, the heart pumps blood about 70 to 100 times per minute. This means the cardiac cycle happens over 100,000 times a day!

Diagram explaining how the heart pumps blood through the cardiac cycle.


The Two Phases of the Cardiac Cycle: Systole and Diastole

To understand how the heart pumps blood, let’s break down the two phases of the cardiac cycle:

1. Systole (Contraction Phase)

Systole is when the heart contracts to pump blood. During this phase:

  • Right ventricle pumps deoxygenated blood to the lungs through the pulmonary artery.
  • Left ventricle pumps oxygenated blood to the body through the aorta.

The ventricles are the key players during systole, as they do the heavy lifting by forcing blood out of the heart. Think of this phase as the heart’s “power stroke” where the ventricles contract to push blood into the arteries.

2. Diastole (Relaxation Phase)

After systole comes diastole, which is when the heart relaxes and fills with blood. During this phase:

  • Blood returns from the body into the right atrium and from the lungs into the left atrium.
  • The atria push blood into the ventricles, filling them up and preparing for the next contraction.

This phase is essential for ensuring that the ventricles have enough blood to pump out during the next heartbeat. It’s the heart’s “refilling” phase.

How Does the Heart Know When to Pump?

Your heart has its own built-in electrical system, which acts like a conductor, telling it when to beat. This system begins at the sinoatrial (SA) node, often called the heart’s natural pacemaker. Here’s how it works:

  1. The SA node sends an electrical signal that causes the atria to contract.
  2. This signal then travels to the atrioventricular (AV) node, which acts as a relay station.
  3. From there, the signal moves down the bundle of His and into the Purkinje fibers, causing the ventricles to contract.

This electrical system ensures that the heart beats rhythmically and that blood is pumped out efficiently. It’s the reason your heart can keep beating on its own, without any conscious effort.

Fun Fact: Your heart continues to beat even if it’s removed from the body for a short time, as long as it has enough oxygen. That’s because of its built-in electrical system!

Blood Flow Through the Heart: A Step-by-Step Process

Now that we understand the phases of systole and diastole, let’s look at how blood flows through the heart during the cardiac cycle.

Step 1: Blood Returns to the Heart

  • Deoxygenated blood from the body returns to the right atrium through the superior and inferior vena cava.
  • Oxygenated blood from the lungs returns to the left atrium through the pulmonary veins.

Step 2: Blood Moves Into the Ventricles

  • During diastole, the atria contract, pushing blood into the right and left ventricles.

Step 3: Ventricles Contract and Pump Blood Out

  • During systole, the right ventricle contracts, pumping deoxygenated blood to the lungs through the pulmonary artery.
  • At the same time, the left ventricle contracts, pumping oxygenated blood to the body through the aorta.

This process happens over and over again, ensuring that your body always has a fresh supply of oxygen-rich blood.

Image Description:

A step-by-step flow chart or diagram showing the flow of blood from the body and lungs into the heart and out to the lungs and body.

Global Data and Indian Context: Heart Disease and the Cardiac Cycle

Heart disease is the leading cause of death worldwide, according to the World Health Organization (WHO), with 17.9 million deaths each year. The situation is even more concerning in India, where 25% of all deaths are due to cardiovascular diseases, as reported by the Indian Heart Association.

One of the biggest challenges is high blood pressure (hypertension), which can damage the heart by making it work harder during the cardiac cycle. In India, 1 in 3 adults suffers from high blood pressure, and many are unaware of their condition. High blood pressure can lead to heart failure, where the heart is unable to pump blood effectively.

Reference for Data:

What Happens When the Heart Can’t Pump Blood Properly?

When the cardiac cycle is disrupted, it can lead to various heart conditions. Let’s explore some of the most common issues:

1. Heart Failure

Heart failure occurs when the heart cannot pump blood efficiently. This can happen because the heart muscle is too weak (systolic heart failure) or too stiff (diastolic heart failure). Over time, high blood pressure, heart attacks, or other conditions can weaken the heart.

  • Symptoms: Shortness of breath, fatigue, swelling in the legs.
  • Indian Context: In India, heart failure affects nearly 10 million people, with the numbers rising due to high rates of hypertension and diabetes.

2. Arrhythmia

An arrhythmia is an irregular heartbeat caused by problems with the heart’s electrical system. It can cause the heart to beat too fast, too slow, or erratically, affecting the cardiac cycle.

  • Symptoms: Palpitations, dizziness, fainting.
  • Indian Context: Arrhythmias are often linked to conditions like diabetes and hypertension, both of which are common in India.

3. Heart Valve Problems

If the heart valves are damaged or don’t open and close properly, it can disrupt blood flow during the cardiac cycle. Conditions like mitral valve prolapse or aortic stenosis can make it harder for the heart to pump blood effectively.

  • Symptoms: Chest pain, shortness of breath, fatigue.
  • Global Data: According to the American Heart Association, 8-10 million people worldwide are affected by valve diseases, including many in India due to poor access to early treatment.

Reference for Data:

How to Keep Your Heart Pumping Smoothly

Now that you know how the heart pumps blood, it’s important to take steps to keep it healthy. Here are some practical tips to support your cardiac cycle and overall heart health:

  1. Monitor Your Blood Pressure: High blood pressure is one of the biggest threats to the heart. Regular monitoring can help you stay ahead of problems. Aim to keep your systolic pressure below 120 mmHg and diastolic pressure below 80 mmHg for optimal heart health.
  2. Stay Active: Exercise helps strengthen your heart and improves blood flow. According to the World Heart Federation, just 30 minutes of daily exercise can reduce your risk of heart disease by 35%.
  3. Eat a Heart-Healthy Diet: Foods rich in fruits, vegetables, and whole grains can help protect your heart. Traditional Indian foods like lentils, spinach, and turmeric are excellent for heart health because they reduce inflammation and improve blood flow.
  4. Manage Stress: Stress puts extra pressure on your heart and can disrupt the cardiac cycle. Practices like yoga and meditation, widely used in India, can help manage stress and improve heart function.

In Conclusion

The cardiac cycle is a finely tuned process that allows your heart to pump blood efficiently throughout your body. Understanding how systole and diastole work, along with how blood flows through the heart, gives you a greater appreciation for this vital organ.

In India, where heart disease rates are rising, taking steps to support your heart health is more important than ever. By maintaining a healthy lifestyle—through regular exercise, a balanced diet, and stress management—you can ensure that your heart keeps pumping smoothly for years to come.

Key Takeaways:

  • The cardiac cycle consists of two phases: systole (when the heart contracts) and diastole (when the heart relaxes).
  • The heart’s electrical system ensures that the heart beats in a rhythmic cycle, allowing efficient blood circulation.
  • Heart disease is the leading cause of death in India, and high blood pressure is a major risk factor.
  • Regular exercise, a heart-healthy diet, and managing stress are key to keeping your heart pumping efficiently.

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