• snuggly enclosed within medistinum
• extends obliquely from 2nd rib to 5th intercostal space
• rests on superior surface of diaphram
• anterior to vertebral column
• posterior to sternum
• lungs flank heart laterally and partially obscure it
• sits at an angle, such that apex points toward left hip and 2/3 of it mass lies to the left of the midsternal line

describe the structure of the pericardial cavity and the pericardial membranes

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• fibrous pericardium
• most superficial
• made of dense fibrous CT 
• protects heart
• anchors it to surrounding structures
• prevents heart from overfilling with blood
• serous pericardium
• deep to fibrous pericardium
• thin, slippery two-layer membrane
• forms closed sac around heart
• parietal layer
• lines internal surface of fibrous pericardium
• attaches to arteries exiting the heart at the heart's superior surface, then turns inferiorly to cover external surface of heart as visceral layer or epicardium
• pericardial cavity
• between the two serous layers
• filled with serous fluid which acts as a lubricant

• compliance means that an increase in volume occurs in a vessel when the pressure in that vessel is increased, or the tendancy of the arteries and veins to stretch in response to pressure.
• blood vessel with higher compliance deform easier than lower compliance vessels under the same pressure and volume conditions. 
• venous compliance is 30 times larger than arterial compliance
• decreased compliance would lead to increased blood pressure

• most superficial of the layers
• is the visceral layer of serous pericardium
• protects the heart

• middle layer
• composed mainly of cardiac muscle 
• bulk of heart
• contractions allow for pumping of the blood

• deepest layer
• made up of simple squamous epithelium
• smooth layer that lines heart chambers, covers difbrous skeleton of valves 
• is continuous with endothelial linings of blood vessles leaving and entering the heart
• allows blood to flow smoothly

gross anatomy of the heart and great vessels

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1. brachiocephalic
2. superior vena cava
3. right pulmonary artery
4. ascending aorta
5. pulmonary trunk
6. right pulmonary veins
7. right atrium
8. right coronary artery
9. anterior cardiac vein
10. right ventricle
11. right marginal artery
12. small cardiac vein
13. inferior vena cava
14. left common carotid
15. left subclavian
16. aortic arch
17. ligamentus anteriosum
18. left pulmonary artery 
19. left pulmonary veins
20. left auricle of left atrium
21. circumflex artery
22. left coronary artery (in coronary sulcus)
23. left ventricle
24. great cardiac vein
25. anterior interventricular artery ( in anterior interventricular sulcus)
26. apex

1. aortic arch
2. left pulmonary artery
3. left pulmonary veins
4. left auricle
5. left atrium
6. great cardiac vein
7. posterior vein of left ventricle
8. left ventricle
9. apex
10. superior vena cava
11. right pulmonary artery
12. right pulmonary veins
13. right auricle
14. inferior vena cava
15. coronary sinus
16. right coronary artery (in coronary sulcus)
17. posterior interventricular artery (in posterior interventricular sulcus)
18. middle cardiac vein
19. right ventricle

1. superior vena cava
2. right pulmonary artery
3. pulmonary trunk
4. right atrium
5. right pulmonary veins
6. fossa ovalis
7. pectinate muscle
8. tricuspid valave
9. right ventricle
10. chordae tendineae
11. trabeculae carneae
12. inferior vena cava
13. aorta
14. left pulmonary artery
15. left atrium
16. left pulmonary veins
17. bicuspid valve
18. aortic valve
19. pulmonary vavle
20. left ventricle
21. papillary muscle
22. interventricular septum
23. epicardium
24. myocardium
25. endocardium

deoxigenated blood flows to

→ superior or inferior vena cava

→ right atrium 

→ tricuspid valve 

→ right ventricle 

→ pulmonary semilunar valve 

→ pulmonary trunk 

→ pulmonary arteries 

→ lungs 

→ pulmonary veins 

→ left atrium 

→ bicuspid valve 

→ left ventricle 

→ arotic semilunar valve 

→ ascending aorta, aortic arch, descending aorta 

→ distributed systematically 

→ re-enter through superior and inferior vena cava

• heart valves make up part of the cardiac skeleton of the heart
• open and close in response to differences in blood pressure and function to keep blood flow unidirectional.
• AV valves  
• located at each atrial-ventricular junction and prevent backflow into the atria when the ventricles contract. 
• When the atria contract and the ventricles are relaxed however, these upside-down-umbrella-like structures open to allow blood to flow into the ventricles.
• aortic and pulmonary SL valves 
• guard the bases of the large arteries issuing from the ventricles (aorta and pulmonary trunk, respectively) 
• prevent backflow into the associated ventricles. 
• Each SL valve is made up of three pocket-like cusps, each shaped roughly like a crescent moon. 
• They respond to differences in pressure, such that when the ventricles contract and the intraventricular pressure becomes greater than the pressure inside the aorta and pulmonary trunk, the SL valves are forced open. When the ventricles relax, some blood naturally tries to exit via the SL valves but as the cusps fill with blood they close and the blood is forced through the arteries. 

• chordae tendineae
• "heart strings"
• made of collagen that anchor AV valves to papillary muscles
• papillary muscles
• anchor AV valve cusps in their closed position with help of chordae tendineae
• just as umbrella can be blown inside out in a gusty wind, so would the AV valve cusps without these structures to keep them in place
• valve cusps
• prevent backflow of blood to keep blood flow unidirectional