1. Anatomy Review of the Human Heart

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Headshot of Chris Anderson, MD · Clinical Education Director, Pediatrics
Chris Anderson
MD · Clinical Education Director, Pediatrics
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Headshot of Kevin Hodges, Vice Chair, Emergency Medicine
Kevin Hodges
Vice Chair, Emergency Medicine
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Table of Contents

Anatomy of the heart: Overview

The human heart is a hollow four-chambered muscle that is responsible for pumping blood throughout the body. The heart lies in the mediastinum in the thorax, pointing toward the left of the midline.

Define and identify the following:

  • Pericardium

  • Myocardium

  • Endocardium

  • Epicardium

  • Circulation

  • Origin and path of the right coronary artery

  • Origin and path of the left coronary artery

  • Branches of the left coronary artery

  • Blood supply to the right ventricle

  • Blood supply to the AV node

  • Blood supply to the septum, anterior wall, lateral walls, posterior wall, and inferior wall of the heart.

The Pericardium

The heart consists of four main layers: The pericardium, epicardium, myocardium, and endocardium. The pericardium is a loose-fitting fibroserous sac that covers the heart. Separating the epicardium (the outermost layer of the heart muscle) from the pericardium is a space called the pericardial space. The space is filled with fluid that acts as a lubricating agent protecting the heart from injuries caused by friction while it is beating.

Layers of the heart

The epicardium is the outermost layer of the heart muscle. It also is known as the visceral pericardium. The middle layer of the heart is called the myocardium. The myocardium is the thick muscular layer of the heart and is responsible for the heart’s ability to contract. The innermost layer of the heart is the endocardium. This layer lines the valves and chambers of the heart.

Heart chambers

The heart is divided into two sides: the right side and the left side. The right side of the heart contains the right atrium and right ventricle. The left side of the heart contains the left atrium and left ventricle. The right and left sides of the heart are anatomically separated by the atrial septum and the ventricular septum. The two sides of the heart could be considered two separate pumps and essentially work independently of each other.

The circulation

The right atrium receives deoxygenated blood from the body via the superior and inferior venae cavae. During diastole, the blood is pushed from the right atrium into the right ventricle. The blood is then forced out of the right ventricle into the pulmonary circulation where it picks up oxygen. The oxygen rich blood is transported into the left atrium via the pulmonary veins. During ventricular diastole, the blood is forced into the left ventricle. The left ventricle pumps the oxygen-rich blood throughout the body.

The heart valves

The heart has four valves that act as tiny doors that keep the blood moving in one direction. The closure of the valves prevents the backward flow of blood. The right atrium and right ventricle are separated by the tricuspid valve and the left atrium and left ventricle are separated by the mitral valve. These valves are known as cuspid valves. The aortic valve lies between the left ventricle and the aorta, and the pulmonic valve separates the right ventricle from the pulmonary artery. The aortic and pulmonic valves are called semilunar valves because of their distinct half-moon appearance.

The coronary circulation

The heart muscle receives oxygen-rich blood via two main vessels: the right coronary artery (RCA) and the left coronary artery (LCA). Both arteries arise from the aortic root. As they travel down the length of the heart, each divides into several branches, as shown below.

The right coronary artery travels along the coronary sulcus, which is the groove between the atria and the ventricles, and continues down the posterior aspect of the ventricular septum. It typically supplies blood to the right ventricle, the atrioventricular (AV) node, part of the septum, as well as to the posterior and inferior walls of the left ventricle.

The left coronary artery consists of two branches, the left anterior descending branch (LAD) and the circumflex branch (CFX).

The LAD artery perfuses the anterior wall of the left ventricle, the anterior section of the ventricular septum, and the lateral wall of the left ventricle.

The CFX branch of the left coronary artery supplies blood to the left atrium and the posterior and lateral walls of the left ventricle.

Coronary arteries as end arteries

The three main branches of the coronary arteries typically do not connect or anastomose with each other at their ends and are therefore called “end arteries.” This anatomical feature poses significant problems when atherosclerotic lesions develop in the arteries, because there is no alternate route for the blood to travel. This leads to ischemia and necrosis of the myocardial tissue.

Although the main coronary arteries are end arteries and do not connect with each other, the smaller arterial vessels can sometimes anastomose to some degree, providing what is known as collateral circulation. If collateral circulation develops, it provides a means of supplying blood to the ischemic areas of the heart. Therefore, the factors surrounding the development of collateral circulation are of great significance in the study and treatment of coronary artery disease.

Case Example 1: Blood supply to the myocardium

The coronary arteries lie on the outermost layer of the heart, or epicardium, and penetrate in toward the myocardium. The portion of myocardium farthest from the artery lies near the endocardium and is called subendocardial tissue. It has the poorest blood supply of the entire myocardium.

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