The oxygenated blood leaving the heart is distributed to:

Upper body: Via the ascending aorta.

Lower body: Via the descending aorta.

Heart: Via the coronary arteries.

The blood enters the heart through the superior and inferior vena cava veins

  The heart is divided into four chambers.

The right side of the heart (RA RV) works to push the blood into the pulmonary vein toward the lungs.

The left side of the heart (LA LV) works to push the blood throughout the body.

However, the top part of the heart, the atria (right/left atrium) contract at the same time, followed by the bottom ventricles which also contract together. 

In other words, the atria contract and then the ventricles contract.

The two sides of the heart are separated by the septum.

Heart Valves

The heart is encased in the pericardium sac

The muscle that does all the work is called the myocardium.

Myocardial infarction, commonly known as a heart attack, is a medical emergency that occurs when blood flow to a part of the heart muscle is blocked. This blockage is typically caused by a blood clot that forms in a coronary artery, one of the arteries that supplies blood to the heart.

When the blood flow is interrupted, the heart muscle becomes deprived of oxygen and nutrients. This can lead to cell death (necrosis) and permanent damage to the heart tissue.

Symptoms of a heart attack can include:

• Chest pain or discomfort, often described as a squeezing or pressure sensation

• Shortness of breath

• Pain in the left arm, shoulder, jaw, or back

• Nausea or vomiting

• Sweating

• Lightheadedness or dizziness

• Sudden weakness or collapse

Treatment for a heart attack typically involves:

• Medication: To dissolve the blood clot, prevent further blood clots, and manage other symptoms.

• Angioplasty: A procedure to open the blocked artery using a balloon and stent.

• Coronary artery bypass graft (CABG): A surgical procedure to bypass the blocked artery using a graft from another part of the body.

Terminology

Depolarization – chamber muscles receive an increase in electrical charge which causes the muscles to contract. (systole -- ‘sis/toe/lee)

Repolarization –  chambers are returning to a resting state (diastole -- die/’ass/toe/lee).

SA node (Sinoatrial node) -- the source of the electrical charge.

AV node (Atrioventricular node) – causes a delay in the electrical charge.

How it works

The basic sequence of events in the heart's electrical conduction system:

1. Initiation:

   • A single electrical charge begins at the SA node. The node is located in the upper part of the atria near the superior vena cava vein.

2. Atrial Conduction:

   • The charge travels through the atria, causing them to contract and push blood into the ventricles.

3. AV Node:

   • The electrical impulse converges at the AV node which is located in the interratrial septum.

   • The AV node delays the charge briefly to allow the atria to fully contract, filling the ventricles with blood.

4. Ventricular Conduction:

   • After the delay, the charge is released and travels through the ventricles, leading to their contraction and expelling the blood into the lungs and body.

A more detailed look

A single electric impulse is initiated by the SA node and travels by a controlled pathway throughout the heart, ensuring a normal heart rhythm.

As stated above, the SA node initiates the heartbeat with an electrical charge. 

The charge is sent to the internodal tracts (anterior, middle, and posterior).

These tracts ensure the electric charge is dispersed throughout the left atrium muscle fibers which cause the atria to contract.

The charge also travels through the Brachmann's bundle to the right atrium for simultaneous contraction of the atria.

This charge is then delayed by the AV node (allowing for the atria to fully contract before initiating the ventricular contraction).

From the AV node, the charge then travels through the AV bundle (bundle of His) then through the bundle branches and into the Purkinje fibers, causing the ventricles to contract.

Here is a labelled chart. Don't panic. We'll go over it piece by piece.

P wave – represents the initial electrical impulse to the atria (depolarization).

PR segment – represents the delayed charge in the AV node.

note: It is called the PR segment because sometimes the Q wave is not present.

PR interval (P wave + PR segment) – represents the full contraction of the atria.

QRS wave – represents the release of the charge from the AV node into the ventricles.

ST segment – represent the contraction of the ventricles.

ST Interval is the ST segment + the T-wave. This interval is not commonly referenced but it is the time that the ventricles move from fully contracted to a state of rest.

T wave – represents the repolarization of the ventricles (returning to a state of rest).

QT interval – full cycle of the ventricle depolarization and repolarization (from full contraction back to a state of rest with some voltage still present).

TP interval – Represent the end of the wave for. The time between heartbeats (a state of rest with minimal voltage present). The waveform starts again at the p wave.

RR interval

The chart again.