Write it Up

The heart is a muscular organ, in all vertebrates responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in annelids, mollusks, and arthropods. The term cardiac (as in cardiology) means "related to the heart" and comes from the Greek καρδία, kardia, for "heart."

The heart of a vertebrate is composed of cardiac muscle, an involuntary muscle tissue which is found only within this organ. The average human heart beating at 72 BPM, will beat approximately 2.5 billion times during a lifetime spanning 66 years.

n the human body, the heart is usually situated in the middle of the thorax with the largest part of the heart slightly offset to the left (although sometimes it is on the right, see dextrocardia), underneath the breastbone (see diagrams). The heart is usually felt to be on the left side because the left heart (left ventricle) is stronger (it pumps to all body parts). The left lung is smaller than the right lung because the heart occupies more of the left hemithorax. The heart is enclosed by a sac known as the pericardium and is surrounded by the lungs. The pericardium comprises two parts: the fibrous pericardium, made of dense fibrous connective tissue; and a double membrane structure containing a serous fluid to reduce friction during heart contractions (the serous pericardium). The mediastinum, a subdivision of the thoracic cavity, is the name of the heart cavity.

The apex is the blunt point situated in an inferior (pointing down and left) direction. A stethoscope can be placed directly over the apex so that the beats can be counted. It is located posterior to the 5th intercostal space in the left mid-clavicular line. In normal adults, the mass of the heart is 250-350 g (9-12 oz), or about three quarters the size of a clenched fist, but extremely diseased hearts can be up to 1000 g (2 lb) in mass due to hypertrophy. It consists of four chambers, the two upper atria (singular: atrium ) and the two lower ventricles.

A heart attack occurs when blood flow to a section of heart muscle becomes blocked. If the flow of blood isn’t restored quickly, the section of heart muscle becomes damaged from lack of oxygen and begins to die.

Heart attack is a leading killer of both men and women in the United States. But fortunately, today there are excellent treatments for heart attack that can save lives and prevent disabilities. Treatment is most effective when started within 1 hour of the beginning of symptoms. If you think you or someone you’re with is having a heart attack, call 9–1–1 right away.

Overview

Heart attacks occur most often as a result of a condition called coronary artery disease (CAD). In CAD, a fatty material called plaque (plak) builds up over many years on the inside walls of the coronary arteries (the arteries that supply blood and oxygen to your heart). Eventually, an area of plaque can rupture, causing a blood clot to form on the surface of the plaque. If the clot becomes large enough, it can mostly or completely block the flow of oxygen-rich blood to the part of the heart muscle fed by the artery.

Heart With Muscle Damage and a Blocked Artery

Figure A is an overview of a heart and coronary artery showing damage (dead heart muscle) caused by a heart attack. Figure B is a cross-section of the coronary artery with plaque buildup and a blood clot.

During a heart attack, if the blockage in the coronary artery isn’t treated quickly, the heart muscle will begin to die and be replaced by scar tissue. This heart damage may not be obvious, or it may cause severe or long-lasting problems.

Severe problems linked to heart attack can include heart failure and life-threatening arrhythmias (irregular heartbeats). Heart failure is a condition in which the heart can’t pump enough blood throughout the body. Ventricular fibrillation is a serious arrhythmia that can cause death if not treated quickly.

Get Help Quickly

Acting fast at the first sign of heart attack symptoms can save your life and limit damage to your heart. Treatment is most effective when started within 1 hour of the beginning of symptoms.

The most common heart attack signs and symptoms are:

• Chest discomfort or pain—uncomfortable pressure, squeezing, fullness, or pain in the center of the chest that can be mild or strong. This discomfort or pain lasts more than a few minutes or goes away and comes back.
• Upper body discomfort in one or both arms, the back, neck, jaw, or stomach.
• Shortness of breath may occur with or before chest discomfort.
• Other signs include nausea (feeling sick to your stomach), vomiting, lightheadedness or fainting, or breaking out in a cold sweat.

If you think you or someone you know may be having a heart attack:

• Call 9–1–1 within a few minutes—5 at the most—of the start of symptoms.
• If your symptoms stop completely in less than 5 minutes, still call your doctor.
• Only take an ambulance to the hospital. Going in a private car can delay treatment.
• Take a nitroglycerin pill if your doctor has prescribed this type of medicine.

Outlook

Each year, about 1.1 million people in the United States have heart attacks, and almost half of them die. CAD, which often results in a heart attack, is the leading killer of both men and women in the United States.

Many more people could recover from heart attacks if they got help faster. Of the people who die from heart attacks, about half die within an hour of the first symptoms and before they reach the hospital.