To understand cardiac physiology, it’s best to view the heart not just as a pump, but as a sophisticated, self-
regulating electromechanical system. It translates electrical signals into physical force to move blood through
two distinct circuits: the pulmonary (lungs) and the systemic (body).
1. The Basics: Anatomy and Circuitry
The heart is divided into four chambers. The atria act as receiving boosters, while the ventricles are the heavy
lifters.
Right Heart: Receives deoxygenated blood and pumps it to the lungs (low pressure).
Left Heart: Receives oxygenated blood and pumps it to the rest of the body (high pressure).
The Valves: Ensure unidirectional flow. The atrioventricular (AV) valves (Tricuspid/Mitral) prevent
backflow into the atria, while the semilunar valves (Pulmonary/Aortic) prevent backflow into the ventricles.
2. Electrical Physiology (The Spark)
Before the muscle contracts, it must be "told" to do so. The heart’s intrinsic conduction system follows a
specific hierarchy:
1. SA Node (The Pacemaker): Located in the right atrium, it sets the rhythm (60–100 bpm).
2. AV Node (The Gatekeeper): It introduces a 0.1-second delay. This is crucial—it allows the atria to finish
contracting and filling the ventricles before the ventricles fire.
3. Bundle of His & Purkinje Fibers: These distribute the signal rapidly to the ventricular apex, ensuring the
contraction starts at the bottom and squeezes blood upward toward the exit valves.
The Cardiac Action Potential
Unlike skeletal muscle, cardiac cells have a "plateau phase" caused by an influx of Calcium ($Ca^{2+}$). This
ensures a long refractory period, meaning the heart cannot undergo tetany (lock up); it must relax between
beats.
3. Cardiac Mechanics: The Cycle
The cardiac cycle is the sequence of events from the beginning of one heartbeat to the beginning of the next. It
is divided into two main phases: Diastole (relaxation/filling) and Systole (contraction/ejection).
The Wiggers Diagram Breakdown
This is the "gold standard" for understanding how pressure, volume, and electrical activity correlate.
Isovolumetric Contraction: The ventricles begin to contract. All valves are closed. Pressure rises
sharply, but volume doesn't change yet.
Ventricular Ejection: Ventricular pressure exceeds aortic pressure; the aortic valve snaps open, and
blood rushes out.
Isovolumetric Relaxation: The ventricle relaxes. All valves are closed again. Pressure drops, preparing
for the next fill.
4. Advanced Mechanics: Hemodynamics
To understand the "depth" of cardiac function, we look at how the heart adapts to demand.
, Frank-Starling Law
This is the heart's "rubber band" effect. The more the heart is stretched during filling (Preload), the more
forcefully it contracts. This ensures that what comes in, goes out.
Key Equations
Stroke Volume (SV): The amount of blood ejected per beat ($SV = EDV - ESV$).
Cardiac Output (CO): The total volume of blood pumped per minute ($CO = HR \times SV$).
Afterload: The "resistance" the heart must pump against (essentially the blood pressure in the arteries).
5. Regulation and Feedback
The heart doesn't work in a vacuum. It is constantly adjusted by:
Autonomic Nervous System: Sympathetic (fight or flight) increases heart rate and contractility;
Parasympathetic (rest and digest) slows it down via the Vagus nerve.
Baroreceptors: Pressure sensors in the carotid sinus that tell the brain if blood pressure is too high or
low.
Note: Efficiency is measured by Ejection Fraction (EF). A healthy heart typically pumps out 55–70% of the
blood in the ventricle with each beat—never 100%.
Gordon Moore, the co-founder of Intel, and his famous eponymous "law" that defined the digital age.
However, depending on your interests, you might be thinking of a few other notable figures.
1. Gordon Moore and "Moore’s Law"
Gordon Moore (1929–2023) was an American engineer and businessman who co-founded Intel. He is best
known for a 1965 observation that became the roadmap for the entire tech industry.
The Law: Moore’s Law is the observation that the number of transistors on a microchip doubles
approximately every two years, while the cost of computers is halved.
The Impact: This exponential growth is why your smartphone today has more computing power than the
room-sized NASA computers that sent humans to the moon.
Is it "Dead"?: While physical limits (like the size of an atom) are slowing down traditional transistor
shrinking, the industry continues to innovate through 3D chip stacking and new materials.
2. In Pop Culture
If you aren't looking for a tech history lesson, you might be thinking of these famous performers:
Demi Moore: An iconic American actress and member of the "Brat Pack" in the 1980s. She became the
highest-paid actress in the world in the mid-90s with hits like Ghost, A Few Good Men, and G.I. Jane.
Most recently, she received critical acclaim for the 2024 body-horror film The Substance.
Dudley Moore (1935–2002): A beloved British actor, comedian, and jazz musician. He is best
remembered for his Oscar-nominated role in Arthur and the comedy classic 10.
3. Other Notable Moores
regulating electromechanical system. It translates electrical signals into physical force to move blood through
two distinct circuits: the pulmonary (lungs) and the systemic (body).
1. The Basics: Anatomy and Circuitry
The heart is divided into four chambers. The atria act as receiving boosters, while the ventricles are the heavy
lifters.
Right Heart: Receives deoxygenated blood and pumps it to the lungs (low pressure).
Left Heart: Receives oxygenated blood and pumps it to the rest of the body (high pressure).
The Valves: Ensure unidirectional flow. The atrioventricular (AV) valves (Tricuspid/Mitral) prevent
backflow into the atria, while the semilunar valves (Pulmonary/Aortic) prevent backflow into the ventricles.
2. Electrical Physiology (The Spark)
Before the muscle contracts, it must be "told" to do so. The heart’s intrinsic conduction system follows a
specific hierarchy:
1. SA Node (The Pacemaker): Located in the right atrium, it sets the rhythm (60–100 bpm).
2. AV Node (The Gatekeeper): It introduces a 0.1-second delay. This is crucial—it allows the atria to finish
contracting and filling the ventricles before the ventricles fire.
3. Bundle of His & Purkinje Fibers: These distribute the signal rapidly to the ventricular apex, ensuring the
contraction starts at the bottom and squeezes blood upward toward the exit valves.
The Cardiac Action Potential
Unlike skeletal muscle, cardiac cells have a "plateau phase" caused by an influx of Calcium ($Ca^{2+}$). This
ensures a long refractory period, meaning the heart cannot undergo tetany (lock up); it must relax between
beats.
3. Cardiac Mechanics: The Cycle
The cardiac cycle is the sequence of events from the beginning of one heartbeat to the beginning of the next. It
is divided into two main phases: Diastole (relaxation/filling) and Systole (contraction/ejection).
The Wiggers Diagram Breakdown
This is the "gold standard" for understanding how pressure, volume, and electrical activity correlate.
Isovolumetric Contraction: The ventricles begin to contract. All valves are closed. Pressure rises
sharply, but volume doesn't change yet.
Ventricular Ejection: Ventricular pressure exceeds aortic pressure; the aortic valve snaps open, and
blood rushes out.
Isovolumetric Relaxation: The ventricle relaxes. All valves are closed again. Pressure drops, preparing
for the next fill.
4. Advanced Mechanics: Hemodynamics
To understand the "depth" of cardiac function, we look at how the heart adapts to demand.
, Frank-Starling Law
This is the heart's "rubber band" effect. The more the heart is stretched during filling (Preload), the more
forcefully it contracts. This ensures that what comes in, goes out.
Key Equations
Stroke Volume (SV): The amount of blood ejected per beat ($SV = EDV - ESV$).
Cardiac Output (CO): The total volume of blood pumped per minute ($CO = HR \times SV$).
Afterload: The "resistance" the heart must pump against (essentially the blood pressure in the arteries).
5. Regulation and Feedback
The heart doesn't work in a vacuum. It is constantly adjusted by:
Autonomic Nervous System: Sympathetic (fight or flight) increases heart rate and contractility;
Parasympathetic (rest and digest) slows it down via the Vagus nerve.
Baroreceptors: Pressure sensors in the carotid sinus that tell the brain if blood pressure is too high or
low.
Note: Efficiency is measured by Ejection Fraction (EF). A healthy heart typically pumps out 55–70% of the
blood in the ventricle with each beat—never 100%.
Gordon Moore, the co-founder of Intel, and his famous eponymous "law" that defined the digital age.
However, depending on your interests, you might be thinking of a few other notable figures.
1. Gordon Moore and "Moore’s Law"
Gordon Moore (1929–2023) was an American engineer and businessman who co-founded Intel. He is best
known for a 1965 observation that became the roadmap for the entire tech industry.
The Law: Moore’s Law is the observation that the number of transistors on a microchip doubles
approximately every two years, while the cost of computers is halved.
The Impact: This exponential growth is why your smartphone today has more computing power than the
room-sized NASA computers that sent humans to the moon.
Is it "Dead"?: While physical limits (like the size of an atom) are slowing down traditional transistor
shrinking, the industry continues to innovate through 3D chip stacking and new materials.
2. In Pop Culture
If you aren't looking for a tech history lesson, you might be thinking of these famous performers:
Demi Moore: An iconic American actress and member of the "Brat Pack" in the 1980s. She became the
highest-paid actress in the world in the mid-90s with hits like Ghost, A Few Good Men, and G.I. Jane.
Most recently, she received critical acclaim for the 2024 body-horror film The Substance.
Dudley Moore (1935–2002): A beloved British actor, comedian, and jazz musician. He is best
remembered for his Oscar-nominated role in Arthur and the comedy classic 10.
3. Other Notable Moores
