Heart Anatomy

Instructor Information

• Name: Brady Little, DVM, MSc

• Subject: Heart Anatomy

Objectives of Study

• Analyze, describe, and apply knowledge of the following topics:

  • Position/orientation of the heart within the canine thorax

  • Surface features of the heart

  • Internal features of the heart

  • Normal blood flow covering pulmonary and systemic circulation

  • Blood supply to the heart muscle

  • Sounds of cardiac auscultation

Heart Anatomy Overview

Orientation of the Heart

• Base: Oriented dorsocranially

• Apex: Points ventrocaudally and to the left

  • Located at the 5th IC (Intercostal) space

Heart Positioning

Ventricles within the Thorax

• Right Ventricle: Positioned cranially, adjacent to the sternum

• Left Ventricle: Positioned more laterally to the left

• Septum: Also crucial in dividing the ventricles

Views of the Heart

Dorsoventral View

• Left View (Auricular Surface)

  • Key Structures:

    1. Left auricle

    2. Pulmonary trunk

    3. Right ventricle

    4. Left ventricle

    5. Right auricle

Right View (Atrial Surface)

• Key Structures:

  1. Right atrium

  2. Caudal vena cava

  3. Aorta

  4. Cranial vena cava

Surface Topography

Coronary Groove

• Function:

  • Separates atria and ventricles

  • Contains coronary vessels

  • Often surrounded by fat

Interventricular Grooves

• Types:

  1. Paraconal interventricular groove

  2. Subsinuosal interventricular groove

Internal Features of the Heart

Right Side of the Heart

Structures:

1. Cusp of right atrioventricular valve (Tricuspid)

2. Chordae tendineae

3. Papillary muscles

4. Pulmonary valve

5. Right auricle

6. Right ventricle

Atrioventricular Valves

• Components:

  • Right AV (Tricuspid) valve

  • Left AV (Mitral) valve

  • Aortic valve

  • Pulmonary valve

• Function:

  • Prevent backflow during systole

  • Operate via papillary muscles and chordae tendineae

Circulatory Systems Overview

Two Separate Circuits

1. Pulmonary Circulation:

• Gas exchange in lungs

2. Systemic Circulation:

• Gas exchange in body cells

Blood Flow Pathway

• Right Atrium: Receives deoxygenated blood

  • From cranial and caudal vena cava

• Right Ventricle: Pumps blood to lungs via pulmonary trunk

• Left Atrium: Receives oxygenated blood from the lungs via pulmonary veins

• Left Ventricle: Pumps blood into systemic circulation through the aorta

Valves and Their Functions

• Pulmonary Semilunar Valve: Prevents backflow during diastole

• Aortic Semilunar Valve: Prevents backflow into the left ventricle

• Right AV Valve: Separates right atrium and ventricle

• Left AV Valve: Separates left atrium and ventricle

Cardiac Auscultation

Points of Maximum Intensity (PMI)

• Left Side Sounds:

  • "P" = Pulmonary valve sound (3rd IC space)

  • "A" = Aortic valve sound (4th IC space)

  • "M" = Mitral sound (5th IC space)

• Right Side Sounds:

  • "T" = Tricuspid sound (4th IC space)

Normal Heart Sounds

• Sound caused by blood stopping at closed valves:

  • S1: Closure of AV valves

  • S2: Closure of semilunar valves

Cardiac Cycle

• First Heart Sound (S1): Closure of atrioventricular valves

• Second Heart Sound (S2): Closure of semilunar valves

• Blood Flow:

  • Through open valves is silent in normal dogs and cats

Abnormal Heart Sounds

• Not normally heard in smaller animals, but can occur during certain conditions such as:

  • Left and Right Ventricular filling during diastole

  • Left and Right Atrial contraction before ventricular contraction

• Associated conditions:

  • Hypertrophic cardiomyopathy in small animals