Key Takeaways
- The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle, with the left ventricle being the strongest chamber
- The cardiac conduction system follows the pathway: SA node -> AV node -> Bundle of His -> bundle branches -> Purkinje fibers
- The right coronary artery (RCA) supplies the right side of the heart and inferior wall; the left anterior descending (LAD) supplies the anterior wall and septum
- Cardiac output equals stroke volume multiplied by heart rate (CO = SV x HR), with a normal adult CO of approximately 5 liters per minute
- Normal adult vital signs: heart rate 60-100 bpm, respiratory rate 12-20 breaths/min, systolic BP 90-140 mmHg
- The tricuspid valve separates the right atrium and ventricle; the mitral (bicuspid) valve separates the left atrium and ventricle
- Deoxygenated blood returns to the heart via the superior and inferior vena cava and enters the right atrium
Cardiovascular Anatomy & Physiology
The cardiovascular system is responsible for circulating blood throughout the body, delivering oxygen and nutrients to tissues, and removing waste products. As an EMT, understanding this system is critical for recognizing and managing cardiac emergencies.
Heart Chambers and Valves
The heart is a four-chambered muscular organ roughly the size of a fist, located in the mediastinum (center of the chest), slightly left of the midline.
| Chamber | Function | Blood Type |
|---|---|---|
| Right Atrium | Receives deoxygenated blood from the body | Deoxygenated |
| Right Ventricle | Pumps blood to the lungs | Deoxygenated |
| Left Atrium | Receives oxygenated blood from the lungs | Oxygenated |
| Left Ventricle | Pumps blood to the entire body | Oxygenated |
The heart has four valves that prevent backflow of blood:
- Tricuspid valve - Between right atrium and right ventricle (3 leaflets)
- Pulmonary (semilunar) valve - Between right ventricle and pulmonary artery
- Mitral (bicuspid) valve - Between left atrium and left ventricle (2 leaflets)
- Aortic (semilunar) valve - Between left ventricle and aorta
Memory tip: Tricuspid is on the Right (both have the letter "R" in the word "tRicuspid"). The mitral valve is also called the bicuspid valve because it has 2 leaflets.
Great Vessels
| Vessel | Role |
|---|---|
| Superior vena cava | Returns deoxygenated blood from the upper body to the right atrium |
| Inferior vena cava | Returns deoxygenated blood from the lower body to the right atrium |
| Pulmonary arteries | Carry deoxygenated blood from the right ventricle to the lungs |
| Pulmonary veins | Return oxygenated blood from the lungs to the left atrium |
| Aorta | Carries oxygenated blood from the left ventricle to the body |
Key concept: The pulmonary arteries are the only arteries in the body that carry deoxygenated blood, and the pulmonary veins are the only veins that carry oxygenated blood.
Blood Flow Through the Heart
Blood flows through the heart in a specific sequence:
- Deoxygenated blood enters the right atrium via the superior and inferior vena cava
- Blood passes through the tricuspid valve into the right ventricle
- The right ventricle pumps blood through the pulmonary valve into the pulmonary arteries
- Blood travels to the lungs for gas exchange (CO2 released, O2 absorbed)
- Oxygenated blood returns to the left atrium via the pulmonary veins
- Blood passes through the mitral valve into the left ventricle
- The left ventricle pumps blood through the aortic valve into the aorta
- Oxygenated blood is distributed to the entire body
Cardiac Conduction System
The heart has its own intrinsic electrical system that controls the heartbeat. This is why the heart can continue to beat even when disconnected from the nervous system.
| Structure | Function | Rate (intrinsic) |
|---|---|---|
| SA node (sinoatrial) | Primary pacemaker, located in the right atrium | 60-100 bpm |
| AV node (atrioventricular) | Delays signal to allow atrial filling, located between atria and ventricles | 40-60 bpm |
| Bundle of His | Conducts impulse from AV node to bundle branches | 40-60 bpm |
| Bundle branches | Right and left branches carry impulse down the interventricular septum | 20-40 bpm |
| Purkinje fibers | Distribute impulse throughout the ventricles, causing contraction | 20-40 bpm |
The conduction pathway: SA node -> AV node -> Bundle of His -> Bundle branches -> Purkinje fibers
Coronary Arteries
The heart muscle (myocardium) requires its own blood supply through the coronary arteries:
| Artery | Region Supplied |
|---|---|
| Left main coronary artery | Branches into LAD and circumflex |
| Left anterior descending (LAD) | Anterior wall of left ventricle, interventricular septum |
| Left circumflex artery | Lateral and posterior walls of left ventricle |
| Right coronary artery (RCA) | Right ventricle, inferior wall, SA node (in ~60% of people), AV node |
The LAD is sometimes called the "widowmaker" because blockage of this artery can cause a massive heart attack affecting a large portion of the left ventricle.
Cardiac Output
Cardiac output (CO) is the amount of blood pumped by the heart per minute:
CO = Stroke Volume (SV) x Heart Rate (HR)
- Stroke volume = amount of blood pumped per beat (average ~70 mL in adults)
- Heart rate = beats per minute
- Normal CO = ~70 mL x 72 bpm = ~5,040 mL/min (~5 L/min)
Factors that affect cardiac output:
- Preload - Volume of blood returning to the heart (stretching of ventricles)
- Afterload - Resistance the heart must pump against (primarily arterial BP)
- Contractility - Strength of cardiac muscle contraction
Normal Vital Signs by Age
| Age Group | Heart Rate (bpm) | Respiratory Rate | Systolic BP (mmHg) |
|---|---|---|---|
| Newborn | 120-160 | 30-60 | 60-80 |
| Infant (1-12 mo) | 100-160 | 25-50 | 70-95 |
| Toddler (1-3 yr) | 90-150 | 20-30 | 80-100 |
| Preschool (4-5 yr) | 80-140 | 20-25 | 80-110 |
| School-age (6-12 yr) | 70-120 | 15-20 | 85-120 |
| Adolescent (13-18 yr) | 60-100 | 12-20 | 90-130 |
| Adult | 60-100 | 12-20 | 90-140 |
Which valve separates the left atrium from the left ventricle?
What is the correct order of the cardiac conduction system?
Which coronary artery is commonly referred to as the "widowmaker"?
A patient has a stroke volume of 70 mL and a heart rate of 80 bpm. What is their cardiac output?
Which of the following is unique about the pulmonary arteries?
What is the normal resting heart rate range for an adult?
Arrange the structures of the cardiac conduction system in the correct order of electrical impulse travel:
Arrange the items in the correct order
Match each heart valve to its correct anatomical location:
Match each item on the left with the correct item on the right