Lots of acronyms - too many at times.

So what do they mean?

AED - Automated External Defibrillator

https://en.wikipedia.org/wiki/Automated_external_defibrillator

An AED is a portable electronic device that automatically diagnoses the life-threatening 

cardiac arrhythmias of ventricular fibrillation and pulseless ventricular tachycardia, 

and is able to treat them through defibrillation, the application of electricity 

which stops the arrhythmia, allowing the heart to reestablish an effective rhythm.

ICD - Implantable Cardioverter-Defibrillator

https://en.wikipedia.org/wiki/Implantable_cardioverter-defibrillator

An ICD is a device implantable inside the body, able to perform cardioversion, defibrillation, 

and (in modern versions) pacing of the heart. 

The device is therefore capable of correcting most life-threatening cardiac arrhythmias. 

The ICD is the first-line treatment and prophylactic therapy for patients at risk 

for sudden cardiac death due to ventricular fibrillation and ventricular tachycardia.

Pacemaker -

https://en.wikipedia.org/wiki/Artificial_cardiac_pacemaker

The primary purpose of a pacemaker is to maintain an adequate heart rate,

either because the heart's natural pacemaker is not fast enough, or because

there is a block in the heart's electrical conductive system.

ICDs and Pacemakers are both surgically implanted, usually on the left side and under the collar bone. 

They may also be found on the upper arm or on the left side of the body between the armpit and the waistline.

ICDs and AED give an electrical shock, when needed.

Pacemakers continually generates electrical impulses to regulate the heart,

but do not "shock" the patient. 

Some combine a pacemaker and defibrillator in a single implantable device. 

Others have multiple electrodes stimulating differing positions within the heart to improve synchronization 

of the lower chambers, or ventricles, of the heart.

ICDs and Pacemakers are about the size of your palm.

AED pads are about the size of your hand.

Your heart is about the size of your fist.

MI - Myocardial Infarction

https://en.wikipedia.org/wiki/Myocardial_infarction

This is commonly known as a heart attack, which occurs when blood flow decreases or stops 

to a part of the heart, causing damage to the heart muscle.

SCA - Sudden Cardiac Arrest

https://en.wikipedia.org/wiki/Cardiac_arrest

Cardiac arrest is a sudden loss of blood flow resulting from the failure of the heart to effectively pump.

A Heart Attack and Cardiac Arrest are not the same.

A Heart Attack is a circulatory, or plumbing, issue.

Cardiac Arrest is an electrical issue.

Not everyone having a heart attack will go into cardiac arrest.

CPR - Cardio Pulmonary Resuscitation

https://en.wikipedia.org/wiki/Cardiopulmonary_resuscitation

CPR is an emergency procedure that combines chest compressions with artificial ventilation 

in an effort to manually preserve intact brain function until further measures are taken 

to restore spontaneous blood circulation and breathing in a person who is in cardiac arrest.

CPR alone is unlikely to restart the heart.

Its main purpose is to restore partial flow of oxygenated blood to the brain and heart. 

The objective is to delay tissue death and to extend the brief window of opportunity 

for a successful resuscitation without permanent brain damage. 

Administration of an electric shock to the subject's heart, termed defibrillation, 

is usually needed in order to restore a viable or "perfusing" heart rhythm.

Defibrillation is effective only for certain heart rhythms, namely ventricular fibrillation 

or pulseless ventricular tachycardia, rather than asystole or pulseless electrical activity.

Early shock, when appropriate, is recommended.

CPR may succeed in inducing a heart rhythm that may be shockable.

In general, CPR is continued until the person has ROSC - a Return Of Spontaneous Circulation 

or is declared dead.

THE CPR GALS has found the following videos which give a good description

on how the heart works.

In a CPR and First Aid Class, you will learn more about the signs and symptoms, 

how aspirin helps a true heart attack victim, how to give proper CPR as well as 

how using an AED help raise the chance of someone surviving.