Physiology of the Heart

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This page is intended to provide working surface knowledge of the heart's anatomy and physiology. Keep in mind that both cardiac and systemic A&P are incredibly information dense topics and that there are doctoral fields of study for each. This page will give an overview of the cardiac system that is sufficient for the majority of paramedics, but it is always recommended to perform your own independent research and study as this page will not cover more in depth topics that may be salient to a paramedic's practice.

Anatomy of the Heart

Figure 1. Diagram of the human heart (cropped)

Walls of the Heart

Endocardium

Myocardium

Pericardium

Chambers of the Heart

Atria

Ventricles

Valves of the Heart

There are four valves of the heart listed in order as the tricuspid, pulmonary semilunar, mitral (bicuspid), and aortic semilunar valves. There is a mnemonic to easily remember these valves and their order: Toilet Paper My Assets. The valves are attached to chordae tendineae and papillary muscles that allow for closure during systole. Malformations or stenosis of valves may cause different heart tones and conditions such as regurgitation; these will not be discussed on this page as they are more in depth topics than a general overview of heart anatomy and physiology will cover.

Arteries and Veins of the Heart

Inferior and Superior Vena Cava

Pulmonary Arteries

Pulmonary Veins

Aorta

Coronary Arteries

Left main coronary artery
Left circumflex coronary artery
Left anterior descending coronary artery
Right coronary artery
- Posterior circulation and dominance

The Flow of Blood

This section will show the flow of blood through cardiac circulation starting at the superior and inferior vena cava. If you have a model or picture of the heart available, you may follow along for ease of visualization.

Blood initially enters cardiac circulation from the superior and inferior vena cava where it pours into the right atrium. As the atria contract, the blood is forced through the tricuspid valve into the right ventricle. The ventricles contract and the blood moves through the pulmonary semilunar valve into the pulmonary trunk of the pulmonary arteries. From there, blood goes through the lungs and is oxygenated in the pulmonary circulatory system before returning to the heart via the pulmonary veins. The pulmonary veins feed into the left atria, and when the atria contract the blood is now forced through the mitral (bicuspid) valve into the left ventricle. From the left ventricle, blood is moved through the aortic semilunar valve into the aorta where it either continues into systemic circulation or "falls back against" the aortic semilunar valve and flows into the coronary arteries to feed the cardiac muscle. The blood is transmitted by the arterial system to a location in the body and exchanges its oxygen for byproducts of cellular metabolism before moving back to the heart via the venous system (of which the last stop is either the superior or inferior vena cava).

Electrical Conduction System

Sinoatrial Node

Internodal Pathways

Bachmann's Bundle

Atrioventricular Node/AV Junction

Bundle of His

Bundle Branches

Left Anterior and Posterior Fascicles

Purkinje Fibers

Cardiac Contraction