❤️ Function of the Heart – The Cardiac Cycle

The heart doesn’t pump randomly—it follows a pattern known as the cardiac cycle. Each heartbeat has three phases:

1️⃣ Diastole (Relaxation Phase)

• Both the atria and ventricles relax.
• Blood from the body and lungs flows into the atria.
• Like a sponge absorbing water passively.

🕐 Time Taken: ~0.4 seconds

2️⃣ Atrial Systole (Atria Contract)

• Atria contract and push blood into the ventricles through the tricuspid and bicuspid valves.
• Like squeezing a water balloon to push water into a container.

🕐 Time Taken: ~0.1 seconds

3️⃣ Ventricular Systole (Ventricles Contract)

• Ventricles contract forcefully, sending blood to the lungs and body.
• Valves close to stop blood from flowing backward.
• Like a powerful push from a piston.

🕐 Time Taken: ~0.3 seconds

🔁 Duration of One Cardiac Cycle

Total time for one heartbeat = 0.8 seconds

• The heart beats about 72 times per minute.

🔢 Over a lifetime: Around 2.5 billion heartbeats! Imagine your heart working every single second from birth till death without ever getting tired.

🔊 Heart Sounds – “Lub-Dub”

Doctors use a stethoscope to hear two main heart sounds:

🔹 “Lubb”

• Occurs when tricuspid and bicuspid valves close.
• Marks the start of ventricular contraction.

🔹 “Dubb”

• Occurs when pulmonary and aortic semilunar valves close.
• Marks the start of ventricular relaxation.

These sounds are normal and indicate healthy valve function.

⚠️ Heart Murmurs

Sometimes, heart valves don’t close properly or become too narrow. This causes blood to flow abnormally, creating a “hissing” sound called a heart murmur.

💡 Example: Imagine if a tap is slightly open and water makes a hissing sound. That’s similar to how a murmur sounds when blood leaks or passes through a narrow valve.

📚 Summary of Key Concepts:

Concept	Explanation
Pulmonary Circulation	Blood flows from heart to lungs and back.
Systemic Circulation	Blood flows from heart to the rest of the body.
Right Side	Handles deoxygenated blood.
Left Side	Handles oxygenated blood.
Cardiac Cycle	The sequence of events in one heartbeat.
Valves	Act like gates to control one-way blood flow.
Lub-Dub	Sounds made by valves closing.
Heart Murmur	Abnormal sound due to faulty valve function.