I. Structure
A. General – hollow cone-shaped muscle; 4 chambers
• Approx. 9 cm X 14 cm
• 2/3 of mass is found on the left side of the body
• Rt. Ventricle- mostly on anterior side
• Lft. Ventricle- mostly on posterior side
B. Walls of the Heart

Pericardium – heart sac, fibrous and parietal layer (outer sac),
pericardial gap; contains serous fluid to reduce friction,
visceral layer (epicardium)

Epicardium – thin outer covering; protection and lubrication

Myocardium – thick middle layer of cardiac muscle which
makes up most of the heart

Endocardium – thin, elastic inner lining made of endothelium
C. Chambers & Valves
 4 chambers:
•
•
•
•
Right Atrium – pump CO2 rich blood to the right ventricle
Right Ventricle – bigger; pumps blood to the lungs
Left Atrium – smaller; pumps blood from lungs to left ventricle
Left ventricle – more muscle mass, pumps O2 rich blood to the
rest of the body
 Valves:
• Tricuspid valve – allows blood right atrium to the right ventricle,
usually 3 flaps
• Bicuspid (mitral) valve – allows blood from the left atrium to the
left ventricle, usually 2 flaps
• Pulmonary (semi-lunar) valve – allows blood to the lungs,
prevents backflow to the right ventricle
• Aortic valve – allows blood from the left ventricle to the aorta,
prevents backflow
Pathway of Blood to and from the Heart
1) Circulated blood from the body (CO2) returns to the heart via the
superior and inferior vena cava  right atrium
2) Right atrium contracts and pumps through the tricuspid valve to
the right ventricle
3) Right ventricle pumps blood through the pulmonary valve to the
lungs
4) In the lungs, CO2 and O2 diffuse through the capillaries and alveoli
5) Oxygenated blood returns from the lungs via the pulmonary vein
6) The left atrium pumps oxygenated blood through the bicuspid
valve to the left ventricle
7) The left side of the heart pumps the hardest to send blood out to
the rest of the body via the aortic valve
•
•
•
Through the carotid artery into the brain
Through the auxiliary arteries into the arms
Through the aorta into the torso and legs
8) Blood moves away from the heart via arteries and capillaries then
returns to the heart through veins
 Cardiac Muscle Tissue
• Striated; consists of sarcomeres just like skeletal muscle
• Cells contain numerous mitochondria (up to 40% of cell volume)
• Intercalated disc: double membrane with two cardiac muscle
cells close together
• Desmosomes: hold the cells tightly together
 Gap Junctions
• Gap junctions: channels that directly connect cytoplasm of the
two cells allows ions and molecules to move easily between
cells.
• low electrical resistance, impulses pass from one cardiac muscle
cell to another
• An action potential originating anywhere in a myocardium will
always be transmitted to all cells of the myocardium
• No gap junctions between atria and ventricles, these cells are
separated by a layer of dense connective tissue that does not
conduct impulses
Electrically
nonconductive
fibrous tissue
Cells of the myocardium
• Contractile cells: require outside stimulus
• Automatic cells: pace-maker cells, contract without stimulus
Areas of Automatic Cells (Intrinsic Conduction System)
1). Sinoatrial (SA) node 2). Atrioventricular (AV) node
3). Atrioventricular (AV) bundle 4). R and L Bundle branches
5). Purkinje fibers
 Cardiac Excitation
• Begins at the SA node & quickly spreads through both atria
• Also travels through the heart's 'conducting system' (AV node > AV
bundle > bundle branches > Purkinje fibers) through the ventricles
• For efficient pumping:
- The atria should contract (& finish contracting) before the ventricles contract.
- The atria should contract as a unit, & the ventricles should contract as a unit.
Blood Circuits
 Pulmonary circuit
•
•
Carries deoxygenated blood from the right side of the
heart to the lungs
Brings oxygenated blood back from the lungs to the left
side of the heart
Blood Circuits
 Systemic circuit
• Carries oxygenated blood from the
left side of the heart to the
rest of the body
• Brings deoxygenated blood back from
the body to the right side of the heart
D) Heartbeat & Blood Pressure
 Stroke Volume (SV) = EDV - ESV
• SV – amount of blood pumped out of each ventricle at each beat, avg.
70mL/beat
• EDV (end diastolic volume) – amount of blood left in ventricles at rest, avg.
120mL/beat (filling up heart with blood)
• ESV (end systolic volume) – amount of blood left after contraction, avg.
50mL/beat (after blood is pumped out how much is left in heart)
 Cardiac output – heart rate x stroke volume
• Amount of blood pumped out per minute, avg. heart rate = 7080 beats/minute
 Blood Pressure – pressure blood exerts on walls of vessels
• Arteries – increase in pressure
• Systolic – max amount of pressure exerted on the walls of
arteries during ventricle contraction (120)
• Diastolic – minimum amount of pressure exerted on the walls of
the arteries during relaxation(80)
 Three important factors affecting blood pressure are:
– Stroke volume (SV)
• amount of blood pumped out by ventricles with each
contraction
– Diameter of the vessel. What happens with big diameter? Low?
• decrease diameter, increase pressure
– Viscosity of blood (thickness of blood). What happens?
• Thinner blood = lower blood pressure
• Thick blood= high blood pressure
 Blood pressure is regulated by
– Autonomic Nervous system- influences the heart rate and
stroke volume
 Blood pressure is maintained through activity of the
– Baroreceptors: stretch receptors in aortic arch and carotid
sinuses
• Increase in blood pressure causes the walls of the vessels to stretch thus
stimulating the nerves to regulate BP
– Chemoreceptors: measure O2, CO2 content of blood, pH of
blood; located in the aortic arch and carotid sinuses
• BP too low, increases CO2, sends signal in order to increases heart rate
and vice versa
Electrocardiography (ECG or EKG) – interpretation of
the electrical activity of the heart
• Depolarization: Electrical activation of the myocardium.
• Repolarization: Restoration of the electrical potential of the
myocardial cell.
 P wave: represents atrial depolarization; Atrial repolarization occurs
during ventricular depolarization and is obscured
 QRS complex: represents ventricular depolarization
 T wave: represents ventricular repolarization
Disorders detected by EKG (http://www.bem.fi/book/19/19.htm)
 Myocardium decreased in size  smaller than normal electric
charge
 Myocardium increased in size  larger than normal electric charge
 Longer P-R interval  conduction problem with SA + AV nodes
 Tachycardia  high heart rate (100b/m); overactive SA node
 Bradycardia  slower heart rate (60b/m); AV node takes over for SA
 Heart Block: damage to AV node; interferes with ventricles
• 1st degree Heart Block  abnormally long P-R wave; delay between atrium +
ventricle
• 2nd degree Heart Block  not all impulses make it to ventricles; skips; 2 P waves
then 2 QRS waves
• Total Heart Block  no impulses to ventricles; uneven ratio of P and QRS waves
 Fibrillation: different arrhythmias; uncoordinated muscle
movement in the heart
• Atrial Fibrillation  no P waves; SA node no longer works; AV node takes
over
• Ventricular Fibrillation  ventricles aren’t depolarizing, only P waves –
cardiac arrest
Diseases
 CAD or CHD (coronary artery/heart disease)
• Full or partial blockage (plaque), lack of oxygen
• Symptoms – shortness of breath, chest pain (angina), coronary
ischemia (reduction of O2 because of reduced blood flow)
• Can be controlled by behavior modifications
• Nitroglycerin + surgery  balloon angioplasty or coronary
artery bypass graph
• Sew femoral + pectoral veins
to bypass blockage
 CABG: Coronary Artery Bypass Grafting
• Most common type of open heart surgery in US
 Myocardial infarction (Heart Attack!)
 A portion of the heart is starved of oxygen = cardiac ischemia
 If cardiac ischemia lasts too long, the starved heart tissue dies
otherwise known as a myocardial infarction -- literally, "death of
heart muscle."
Symptoms
• Chest pain or discomfort (angina pectoris). Most heart attacks involve
discomfort in the center or left side of the chest. The discomfort usually lasts
more than a few minutes or goes away and comes back. It can feel like pressure,
squeezing, fullness, or pain. It also can feel like heartburn or indigestion.
• Upper body discomfort. You may feel pain or discomfort in one or both
arms, the back, shoulders, neck, jaw, or upper part of the stomach (above the
belly button).
• Shortness of breath. This may be your only symptom, or it may occur before
or along with chest pain or discomfort. It can occur when you are resting or
doing a little bit of physical activity.
• Breaking out in a cold sweat
• Feeling unusually tired for no reason, sometimes for days
(especially if you are a woman)
• Nausea (feeling sick to the stomach) and vomiting
• Light-headedness or sudden dizziness