How the Heart Works

Blood that has circulated through the body moves through the right side of the heart into the lungs where oxygen is attached to blood cells. The oxygen-rich blood then pumps back into the other half of the heart and is squeezed out to the rest of the body, and then back to the right side of the heart again.  When the body’s activity requires more oxygenated blood (during exercise or other exertion) the heart beats faster, resulting in a higher heart rate (pulse).  The top chambers of the heart are pumps called the atria. The bottom chambers are pumps called ventricles. These chambers are connected by valves. If a valve leaks or doesn’t open fully, the pumping function can be reduced.

The heart’s function is gauged by the amount of blood it pumps. Normally the heart pumps 60-70 percent of the blood in it. This is called the ejection fraction or EF. When the muscle is weak or damaged, the EF falls. We consider the function to be severely reduced when the EF falls to 20 percent or below.

How is Heart Failure Evaluated? 

The more damage your heart has, the more severe your symptoms will be. You may only experience symptoms such as shortness of breath with strenuous exercise if your heart failure is mild, but with severe heart failure you may be extremely short of breath and weak after minimal exertion. 

The severity of heart failure is measured by the degree of fatigue or shortness of breath experienced when the heart is required to work harder. These are grouped according to a list published by the New York Heart Association:

• Class I - No limitation of physical activity. Ordinary physical activity does not cause undue fatigue, palpitation, shortness of breath or cardiac pain.
• Class II - Slight limitation of physical activity. Comfortable at rest, but ordinary physical activity results in fatigue, palpitation, shortness of breath or chest pain.
• Class III - Marked limitations of physical activity. Comfortable at rest, but less than ordinary activity causes fatigue, palpitations, shortness of breath or chest pain.
• Class IV - Unable to carry out physical activity without discomfort. Symptoms of heart failure or of cardiac pain may be present even at rest. If any physical activity is undertaken, discomfort is increased.

What is a Heart Attack?

Myocardial infarction, or heart attack, occurs when the heart arteries are blocked or partially blocked so that enough blood cannot flow into the heart to maintain its pumping function.  When the blockages are severe, some heart cells die.