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• Heart


  Hollow, muscular, four-chambered organ located in the mediastinum (between the lungs, middle of the thoracic cavity)

  
• Heart


  • Size of a clenched fist and weighs approximately 255 g (9 oz) in women and 310 g (10.9 oz) in men
  • Extends vertically from the left second to the left fifth intercostal space (ICS)
  • Extends horizontally from the right edge of the sternum to the left midclavicular line (MCL)
  • Base is the upper portion, near the left second ICS
  • Apex is the lower portion, near the left fifth ICS and the left MCL
  • Precordium is the anterior chest area that overlies the heart and great vessels

  
• Right side of the heart


  Pumps blood to the lungs for gas exchange (pulmonary circulation) by removing CO2 from blood and replenishing oxygen supply
• Left side of the heart


  Pumps blood to all other parts of the body (systemic circulation)
• Great Vessels


  Large veins and arteries leading directly to and away from the heart
• Great Vessels


  • Superior and inferior vena cava
  • Pulmonary artery
  • Pulmonary veins
  • Aorta
• Right and left atria


  Upper chambers, thin-walled, receive blood returning to the heart and pump blood into the ventricles
• Right and left ventricles


  Lower chambers, thicker-walled, pump blood out of the heart
• Septum


  Partition that separates the right and left sides of the heart
• Atrioventricular (AV) valves


  Located at the entrance to the ventricles, allow blood to flow from the atria into the ventricles but prevent regurgitation back into the atria
• Atrioventricular (AV) valves


  • Tricuspid valve is composed of three cusps and is located between the right atrium and the right ventricle
  • Bicuspid (mitral) valve is composed of two cusps and is located between the left atrium and the left ventricle
  • Chordae tendineae are collagen fibers that anchor the AV valve flaps to papillary muscles within the ventricles
• Semilunar valves


  Located at the exit of each ventricle at the beginning of the great vessels, have three cusps that look like half-moons
• Semilunar valves


  • Pulmonic valve is located at the entrance of the pulmonary artery as it exits the right ventricle
  • Aortic valve is located at the beginning of the ascending aorta as it exits the left ventricle
• Pericardium


  Tough, inextensible, loose-fitting, fibroserous sac that attaches to the great vessels and surrounds the heart

  
• Layers of the heart wall


  • Parietal pericardium
  • Epicardium
  • Myocardium
  • Endocardium

  
• Cardiac muscle cells


  Spontaneously generate an electrical impulse and conduct it through the heart
• Cardiac cycle


  The filling and emptying of the cardiac chambers regulated by sections of the myocardium which generates and conducts electrical impulses
• Sinoatrial (SA) node (or sinus node)


  Pacemaker of the heart, located on the posterior wall of the right atrium near the junction of the superior and inferior vena cava, generates impulses that are conducted over both atria
• Atrioventricular (AV) node


  Slightly delays incoming electrical impulses from the atria and then relays the impulse to the AV bundle (bundle of His) in the upper interventricular septum
• Although the SA node functions as the "pacemaker of the heart," this activity shifts to other areas of the conduction system, such as the Bundle of His (with an inherent discharge of 40-60/min), if the SA node cannot function
• Electrocardiography (ECG or EKG)


  Records the depolarization and repolarization of the cardiac muscle
• Phases of the electrocardiogram

  • P wave
  • PR interval
  • QRS complex
  • ST segment
  • T wave
  • QT interval
  • U wave

  
• Diastole


  Relaxation of the ventricles, known as filling
• Diastole


  1. AV valves are open and the ventricles are relaxed

  2. Higher pressure in the atria than in the ventricles, blood rushes through the atria into the ventricles

  3. Early or protodiastolic filling - early, rapid, passive filling followed by a period of slow passive filling

  4. Presystole, atrial systole, or sometimes the atrial kick - final active filling phase that raises left ventricular pressure
• Systole


  Contraction of the ventricles, known as emptying
• Systole


  1. AV valves (mitral and tricuspid) shut due to pressure in the ventricles to be higher than in the atria

  2. Closure of the AV valves produces the first heart sound (S1)

  3. High pressure inside the ventricles causes the aortic valve to open on the left side and the pulmonic valve to open on the right side

  4. With ventricular emptying, the ventricular pressure falls and the semilunar valves close, producing the second heart sound (S2)

  5. After closure of the semilunar valves, the ventricles relax and atrial pressure is now higher than the ventricular pressure, causing the AV valves to open and diastolic filling to begin again
• Heart sounds


  Produced by valve closure, opening of valves is silent, characterized as "lub-dub" (S1 and S2)
• S1


  • May be heard over the entire precordium but is heard best at the apex (left MCL, fifth ICS)
  • If heard as two sounds, the first component represents mitral valve closure (M1) and the second component represents tricuspid closure (T1)
• S2


  • Heard best at the base of the heart
  • If heard as two sounds, the first component represents aortic valve closure (A2) and the second component represents pulmonic valve closure (P2)
  • Split S2 may be exaggerated during inspiration and disappear during expiration
• S3 and S4


  Referred to as diastolic filling sounds, or extra heart sounds, result from ventricular vibration secondary to rapid ventricular filling

  
• Murmurs


  Blood normally flows silently through the heart, but conditions that contribute to turbulent blood flow can be auscultated over the precordium
• Cardiac Output


  Amount of blood pumped by the ventricles in a minute, calculated as Stroke Volume x Heart Rate
• Stroke Volume


  • Amount of blood pumped from the heart with each contraction, usually 70 mL from the left ventricle
  • Influenced by degree of stretch of the heart muscle (preload), pressure against which the heart muscle has to eject blood (afterload), synergy of contraction, compliance or distensibility of the ventricles, and contractility or the force of contraction
• Factors that contribute to turbulent blood flow


  • Increased blood velocity
  • Structural valve defects
  • Valve malfunction
  • Abnormal chamber openings
• Turbulent blood flow may be auscultated over the precordium
• Cardiac Output


  Amount of blood pumped by the ventricles in a minute
• The normal adult Cardiac Output is 5 to 6 L/min
• Stroke Volume


  Amount of blood pumped from the heart with each contraction
• Stroke Volume from the left ventricle is usually 70 mL
• Factors that influence Stroke Volume


  • Degree of stretch of the heart muscle up to a critical length before contraction (preload)
  • Pressure against which the heart muscle has to eject blood during contraction (afterload)
  • Synergy of contraction
  • Compliance or distensibility of the ventricles
  • Contractility or the force of contractions of the myocardium