The heart is a hollow muscular organ that acts as a pump to circulate blood through the cardiovascular system. It has four chambers - two atria that receive blood and two ventricles that pump blood out. The heart continuously pumps around 4-6 liters of blood in a closed circulatory system. It is divided into a conduction system that generates electrical impulses to contract the heart muscles, and four circuits - pulmonary, systemic, and coronary - that ensure blood flows to and from the lungs and body.

1. PHYSIOLOGY OFTHE HEART

2. INTRODUCTION
The heart is a hollow muscular organ made of specialised cells that
allow it to act as a pump within the circulatory system
Primary Function is to drive blood through the cardiovascular
system delivering :
•Oxygenated blood to the tissues and organs of the body
sufficient for their metabolic needs
•Deoxygenated blood to the lungs for gaseous exchange
The average human adult has 4-6 litres of blood repeatedly
cycled throughout the body in a closed circulatory system.
It is called a closed system because the blood is contained
within the heart and blood vessels at all time and blood always
flows in a forward direction.

3. Structure of Heart
Human heart is divided into 4 chambers
•2 Atria and 2 Ventricles – these are hollow chambers which
receive blood
•They are surrounded by myocardial cells which are able to
relax and contract
•The cardiovascular system consists of circuits:
•Pulmonary circuit provides blood flow between the heart and
lungs
•Systemic circuit allows blood to flow to and from the rest of
the body
•Coronary circuit provides blood to the heart
•The heart valves ensure that blood flows in one direction
through the system
The Heart is:
•Located between the lungs in the centre and to the left of the
midline
•It’s cone shaped and about the size of your own clenched fist
•Can never stop pumping

4. Conduction System
There are 2 basic types of cardiac cell (Myocytes)
1. Myocardial cells
• Contractile
• respond to an electrical impulse and contract
2. Specialised cells
• the conduction system generates electrical impulses and
transmits them through the myocardium

5. Action potential in cardiac muscles

6. Action Potential in Cardiomyocites and
Pacemaker cell

7. Cardiac Cycle

8. Wiggers Diagram

9. Graphical Analysis ofVentricular Pumping
“The volume-pressure curve"
“
■ Figure 9-8 shows a diagram that is especially useful in
explaining the pumping mechanics of the left
ventricle.
■ The most important components of the diagram are
the two curves labeled “diastolic pressure” and
“systolic pressure.”
■ The diastolic pressure curve is determined by filling
the heart with progressively greater volumes of blood
and then measuring the diastolic pressure
immediately before ventricular contraction occurs,
which is the end-diastolic pressure of the ventricle.
■ The systolic pressure curve is determined by
recording the systolic pressure achieved during
ventricular contraction at each volume of filling.

10. “Volume-Pressure Diagram” During the Cardiac Cycle
■ Phase I: Period of filling.
This phase in the volume- pressure diagram begins at a ventricular volume of
about 50 ml and a diastolic pressure of 2 to 3 mm Hg.The amount of blood that
remains in the ventricle after the previous heartbeat, 50 ml, is called the end-
systolic volume. As venous blood flows into the ventricle from the left atrium, the
ventricular volume normally increases to about 120 ml, called the end-diastolic
volume, an increase of 70 ml.
■ Phase II: Period of isovolumic contraction.
During isovolumic contraction, the volume of the ventricle does not change
because all valves are closed. However, the pressure inside the ventricle increases
to equal the pressure in the aorta, at a pressure value of about 80 mm Hg, as
depicted by point C.
■ Phase III: Period of ejection.
During ejection, the systolic pressure rises even higher because of still more
contraction of the ventricle. At the same time, the volume of the ventricle
decreases because the aortic valve has now opened and blood flows out of the
ventricle into the aorta.Therefore, the curve labeled “III,” or “period of ejection,”
traces the changes in vol- ume and systolic pressure during this period of ejection.
■ Phase IV: Period of isovolumic relaxation.
At the end of the period of ejection (point D), the aortic valve closes, and the
ventricular pressure falls back to the diastolic pressure level.The line labeled “IV”
traces this decrease in intraven- tricular pressure without any change in volume.
Thus, the ventricle returns to its starting point, with about 50 ml of blood left in
the ventricle and at an atrial pressure of 2 to 3 mm Hg.

11. Cardiac Output
This is the total volume of blood that is pumped through the heart in a minute.

12. StrokeVolume

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