1. Basic Cardiac
The
Heart

2. The Heart
• To understand the ECG, it helps to understand
the heart and how the heart works

3. The Heart
• Fun Fact
– The average heart beats 100,000 times, pumping
about 2,000 gallons of blood each day!!

4. The Heart
• Fun Fact
– The adult heart weighs approximately 11oz and is
about the size of its owner’s fist
• A person’s heart size and weight are influenced by their
age, body weight and build, frequency of physical
exercise, and heart disease

5. The Heart
• Your heart is a muscular organ that acts like a
pump to send blood throughout your body
• Your heart is located under the ribcage in the
center of your chest between your right and
left lung
• Your heart is at the center of your circulatory
system, which delivers blood to all areas of
your body

6. The Heart
• Your Heart is vital to your health and nearly
everything that goes on in your body
– Without the heart’s pumping action, blood can’t
circulate within your body
• Your blood carries the oxygen and nutrients
that your organs need to function normally.
– Blood also carries carbon dioxide, a waste
product, to your lungs to be passed out of your
body and into the air

7. The Heart
• Pericardium
– Protective sac that surrounds the heart
• Within the pericardium is about 10 mL of serous fluid
that acts as a lubricant, preventing friction as the heart
beats

8. Heart Chambers
• The inside of your heart is divided into four
chambers

9. Heart Chambers
• The two upper chambers of your heart are
called atria
• The atria receive and collect blood

10. Heart Chambers
• The right atrium
– Receives deoxygenated blood returning from the
body through the inferior and superior vena cavae
and from the heart through the coronary sinus

11. Heart Chambers
• The left atrium
– Receives oxygenated blood from the lungs
through the four pulmonary veins

12. Heart Chambers
• The interatrial septum divides the chambers
and helps them contract
• Contraction of the atria forces blood into the
ventricles below

13. Heart Chambers
• The two lower chambers of your heart are
called ventricles
• The ventricles pump blood out of your heart
into the circulatory system to other parts of
your body

14. Heart Chambers
• Right ventricle
– Receives blood from the right atrium and pumps it
through the pulmonary arteries to the lungs,
where it picks up oxygen and drops off carbon
dioxide

15. Heart Chambers
• Left ventricle
– Receives oxygenated blood from the left atrium
and pumps it through the aorta and then out to
the rest of the body

16. Heart Chambers
• The right and left sides of your heart are
divided by an internal wall of tissue called the
septum

17. Great Vessels
• There are blood vessels attached to the heart
that transport blood to and from the lungs
and body
– Pulmonary arteries and veins
– Aorta
– Superior and inferior vena cava

18. Great Vessels
• Pulmonary arteries and veins
– Transfer blood between the heart and lungs

19. Great Vessels
• Aorta
– Delivers oxygenated blood from the heart to the
body

20. Great Vessels
• Superior and Inferior Vena Cava
– Send unoxygenated blood from the body to the
heart

21. The Heart as a Pump
• The left side
– Pumps oxygenated blood and nutrients to the
body’s organs, muscles, and tissues
• The right side
– Pumps deoxygenated blood to the lungs to
exchange carbon dioxide for oxygen

22. Heart Valves
• With each heartbeat, the heart relaxes and
contracts
• During relaxation
– The heart relaxes and fills with blood
• During contraction
– The heart squeezes and pumps blood out to the
body

23. Heart Valves
• For the heart to function properly, your blood
flows in only one direction
– Your heart’s valves make this possible

24. Heart Valves
• The valves make sure the blood travels in only
one direction
Blood travels
from the body
to the right
atrium
Through the Through the
aortic valve into tricuspid valve
the aorta and into the right
out to the body ventricle
Traveling into
Through the
the left atrium,
pulmonic valve
through the
into the
mitral valve into
pulmonary
the left
arteries
ventricle

25. Heart Valves
• Healthy valves open and close in very exact
coordination with the pumping action of your
heart’s atria and ventricles
• When your heart beats, the valves make a
“LUB-DUB” sound that can be heard with a
stethoscope

26. Heart Valves
• Four Valves of the Heart
– Aortic
– Mitral
– Pulmonary
– Tricuspid

27. Heart Valves
• Tricuspid valve
– Regulates blood flow between the right atrium
and right ventricle

28. Heart Valves
• Pulmonary valve
– Controls blood flow from the right ventricle into
the pulmonary artery, which carries blood to your
lungs to pick up oxygen

29. Heart Valves
• Mitral valve
– Lets oxygen-rich blood from your lungs pass from
the left atrium into the left ventricle

30. Heart Valves
• Aortic valve
– Opens the way for oxygen-rich blood to pass from
the left ventricle into the aorta, your body’s
largest artery, where it is delivered to the rest of
your body

31. Heart Valves
Atrioventricular (AV) Semilunar (SL)
• Tricuspid valve • Pulmonic valve
– Right side of the heart – Right side of the heart
– Separates right atrium and – Between right ventricle and
right ventricle pulmonary artery
• Mitral valve (bicuspid) • Aortic valve
– Left side of the heart – Left side of the heart
– Separates left atrium and left – Between left ventricle and
ventricle aorta

32. Coronary circulation
• The heart has it’s own circulatory system to
supply it with oxygen (coronary arteries) and
to remove deoxygenated blood (coronary
veins)

33. Myocardial Ischemia and Infarction
• Myocardial ischemia
– Occurs when the flow of blood through a coronary
artery is decreased, the cardiac muscle tissue fed
by the coronary artery is deprived of oxygen and
nutrients

34. Myocardial Ischemia and Infarction
• Myocardial Infarction (MI) or Heart Attack
– Occurs when one of the arteries that supplies the
heart muscle becomes blocked
– Blockage may be caused by spasm of the artery or
by atherosclerosis with acute clot formation
– The blockage results in damaged tissue and a
permanent loss of contraction of this portion of
the heart muscle

35. Layers of the Heart Wall
• The heart wall is made up of three tissue
layers
– Epicardium
– Myocardium
– Endocardium

36. Layers of the Heart Wall
• Epicardium
– Is the external or outer layer of the heart. This is
where the coronary arteries and veins are found

37. Layers of the Heart Wall
• Myocardium
– Is the middle and thickest layer of the heart and is
responsible for the contraction of the heart

38. Layers of the Heart Wall
• Endocardium
– Is the innermost layer of the heart

39. Cardiac Cells
• There are two basic types of cardiac cells in
the heart:
– Pacemaker
– Myocardial cells

40. Cardiac Cells
• Pacemaker cells (electrical cells)
– Responsible for the spontaneous generation and
conduction of electrical impulses
– Found in the electrical conduction system of the
heart

41. Cardiac Cells
• Myocardial cells (working cells)
– Contain contractile filaments that are
interconnected
– When electrically stimulated, the filaments slide
together and the myocardial cell contracts
– These cells form the myocardium (muscular layer
of the heart)
– These are the working cells and are responsible
for contraction and relaxation

42. Properties of Cardiac Cells
• Automaticity
– Is the ability of the pacemaker cells to
spontaneously initiate an electrical impulse. Only
pacemaker cells have the property of automaticity
– fires impulses regularly
• Contractility
– Refers to the ability of the myocardial cells to
shorten causing cardiac muscle contraction in
response to an electrical stimulus

43. Properties of Cardiac Cells
• Conductivity
– Is a property that refers to the ability of all cardiac
cells to receive and conduct an electrical impulse
to an adjacent cardiac cell
• Excitability
– Refers to the electrical irritability of all cardiac
cells because of an ionic imbalance across the
membranes of cells

44. Properties of Cardiac Cells
Type of Cardiac Cell Where Found Primary Function Properties
Myocardial cells Myocardium Contraction and Contractility
“working cells” relaxation Excitability
Pacemaker cells Electrical Generation and Automaticity
“Electrical cells” conduction system conduction of Conductivity
electrical impulses Excitability

45. Autonomic Nervous System Effects on
the Heart
• The nervous system innervates the heart and
alters the heart rate, force of contraction,
cardiac output, and blood pressure when
stimulated

46. Autonomic Nervous System Effects on
the Heart
• Parasympathetic nerve fibers
– Originate from the inhibitory center of the brain
via the vagus nerve
• Stimulation of this nerve causes the release of
acetylcholine, which decreases the heart rate, force of
contraction, cardiac output , and blood pressure

47. Autonomic Nervous System Effects on
the Heart
• Sympathetic nerve fibers
– Originate from the accelerator center in the brain
– Stimulation of these nerve fibers results in the
release of norepinephrine, which increases the
heart rate, force of contraction, cardiac output,
and blood pressure

48. Understanding the Heart’s Electrical
System
• The heart has an internal electrical system that
controls the speed and rhythm of the heartbeat.
• With each heartbeat, an electrical signal spreads
from the top of the heart to the bottom
• As it travels, the electrical signal causes the heart
to contract and pump blood
• The process repeats with each new heartbeat
• A problem with any part of this process can cause
an arrhythmia

49. Understanding the Heart’s Electrical
System

50. Understanding the Heart’s Electrical
System
• The normal conduction Pathway
– The SA node fires causing atria to contract and pump
blood into the ventricles
– The impulse travels through the atria to the AV node
• The AV node briefly delays the impulse allowing time for the
ventricles to fill with blood
– The impulse then travels through the Bundle of HIS,
right and left bundle branches and Purkinje fibers
• Causing the ventricles to contract
– The ventricles then relax, then the heartbeat process
starts all over again in the SA node
– Youtube: The Heart's electrical system (0.27)

51. Parts of the Electrical Conduction
System
• SA node
• AV node
• Bundle of His
• Right and Left Bundle Branches
• Purkinje Fibers

52. Parts of the Electrical Conduction
System
• SA (Sino-atrial) node
– Located in the right upper atrium
– Called the normal pacemaker of the heart
• It initiates the electrical impulse that is sent through
the heart

53. Parts of the Electrical Conduction
System
• AV (atrioventricular) node
– Located in the lower right atrium and functions as
a “gatekeeper” to the ventricles
– It delays the impulses from the SA node and atria
for a fraction of a second before sending the
impulse to the ventricles
– It also will prevent extra beats from being
conducted to the ventricles

54. Parts of the Electrical Conduction
System
• Bundle of His
– Directly attached to the AV node and extends
from the top left corner of the right ventricle to
the top of the intraventricular septum
– It sends the impulses from the AV node rapidly to
the lower part of the conduction system in the
ventricles

55. Parts of the Electrical Conduction
System
• Right and Left Bundle Branches
– Divided from the Bundle of His
– Found in the intraventricular septum and across
the lower portion of the right and left ventricles

56. Parts of the Electrical Conduction
System
• Purkinje Fibers
– Subdivided into smaller fibers from the right and
left bundle branches
– Distribute the electrical impulse from the bundle
branches to the individual muscle cells in the
ventricles

57. Understanding the Heart’s Electrical
System
• The normal conduction Pathway
– The SA node fires causing atria to contract and pump
blood into the ventricles
– The impulse travels through the atria to the AV node
• The AV node briefly delays the impulse allowing time for the
ventricles to fill with blood
– The impulse then travels through the Bundle of HIS,
right and left bundle branches and Purkinje fibers
• Causing the ventricles to contract
– The ventricles then relax, then the heartbeat process
starts all over again in the SA node
– Youtube: The Heart's electrical system (0.27)

58. Pacemaker Sites of the Conduction
System
• There are three intrinsic pacemaker sites
within the conduction system
• Each site can produce an electrical impulse or
impulses and control the heart rate

59. Pacemaker Sites of the Conduction
System
• The intrinsic rate of each site is as follows:
– SA node
• 60-100 bpm
– AV junction
• 40-60 bpm
– Ventricles
• 20-40 bpm

60. Pacemaker Sites of the Conduction
System
• Normally, the SA node is the pacemaker of the
heart
– If the sinus node slows down or fails to initiate
depolarization (contraction), either the AV
junction or the ventricles will spontaneously
produce electrical impulses

61. The Cardiac Cycle
• The period from the beginning of one
heartbeat to the beginning of one heartbeat
to the beginning of the next one
• Consists of 2 events
– Mechanical
– Electrical

62. The Cardiac Cycle
• Mechanical Events
– The mechanical part of the cardiac cycle is divided
into two phases: diastole (rest) and systole
(contraction). The atria and ventricles contract
and relax in tandem to effectively pump blood
through the heart

63. The Cardiac Cycle
• Mechanical Events
– During atrial systole (contraction) and ventricular
diastole (relaxation), the atria conract and squeeze
blood into the ventricles
– The ventricles are “at rest” and fill with blood

64. The Cardiac Cycle
• Mechanical Events
– During atrial diastole (relaxation) and ventricular
systole (contraction), the atria are “at rest” and fill
with blood, while the ventricles contract and
squeeze blood out of the heart

65. The Cardiac Cycle
• Electrical Events
– The electrical events that occur in the heart
muscle are called depolarization and
repolarization
– The exchange of electrolytes (minerals in your
body that carry an electric charge) across
myocardial cell walls creates the electrical events
that stimulate the heart muscle to contract
– The major electrolytes that affect cardiac function
are sodium and potassium

66. The Cardiac Cycle
• Electrical Events
– Depolarization is the formation and spread of
electrical activity in the heart
– During depolarization, the inside of the cell
becomes more positive
– Depolarization results in contraction of the heart
muscle
– During depolarization, the cardiac cells are in a
refractory state, which means that they are
resistant to additional electrical activity

67. The Cardiac Cycle
• Electrical Events
– Repolarization is the return of the cells to the
resting or polarized state
– During repolarization, the inside of the cell
becomes more negatively charged
• Known as the recovery phase
– Repolarization results in relaxation of the heart
muscle