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ARNICLES

DIAGNOSING HEART DISEASE: EXTERNAL EXAMINATION

THE IMPENDING HEART ATTACK AND THE ACUTE STAGE: WHAT SHOULD THE PATIENT AND RELATIVES NOT DO?

THE HEART'S WORK

HEART DISEASE: VISITING YOUR PHYSICIAN

THE IMPENDING HEART ATTACK AND THE ACUTE STAGE: WHAT CAN RELATIVES DO IF A HEART ATTACK IS SUSPECTED?

THE MYOCARDIUM (HEART MUSCLE): THE CARDIAC CYCLE

SYMPTOMS OF HEART DISEASE: BREATHLESSNESS, HEARTBEAT AND FAINTING

THE IMPENDING HEART ATTACK AND THE ACUTE STAGE: THE DANGERS OF THE FIRST HOURS

THE MYOCARDIUM (HEART MUSCLE): THE ATRIA & THE VENTRICLES

THE HEART VALVES: LOCATION AND STRUCTURE OF THE VALVES

THE HEART'S WORK

No matter how forceful the contraction, your heart does not pump blood out of the ventricles with each beat. The portion of blood 1 pumped out of a filled ventricle is referred to as the ejection fraction. A normal ejection fraction is 50 percent or more; this value indicates that at least half the blood in the ventricle is pumped out on each beat. The ejection fraction is a good indicator of the overall function of the heart pump. In a healthy person, the ejection fraction increases about 5 percent with exercise. When ventricles are diseased, the ejection fraction can diminish to 20 to 30 percent or lower.

The actual amount of blood pumped by the left ventricle with one contraction is called the stroke volume. The stroke volume and the number of times the heart beats per minute (the heart rate) determine the cardiac output, which is the amount of blood the heart pumps through the circulatory system in 1 minute.

The heart has an automatic mechanism to ensure that it pumps out the same amount of blood that it receives. When more blood enters the heart, the cardiac muscle is stretched more. The more the muscle is stretched, the more forceful will be the contraction, and the more blood will be pumped with each beat. Imagine what would happen without this simple but vital adjustment mechanism. If the heart took in just a tiny bit more blood than it pumped out on each beat, it would gradually swell to the point of being unable to function.

The heart can also increase the amount of blood it pumps by beating more times per minute, within limits. When the heart beats very fast, the strength of the heart muscle decreases and the period of diastole (when heart relaxes between contract and fills with blood) becomes too s for the heart chambers to fill adequately.

Although the pumping action of the heart seems simple, the mechanisms that make the pump perform are complex and elegant.

Amount of blood the heart pumps per minute*

Normal output = 5 to 6 liters (a liter is roughly equivalent to a quart)

Output without atria contracting = 4 to 6 liters Output of weakened heart with atria contracting =3 1/2 liters

Output of weakened heart without atria contracting = 2 1/2 liters

*27\252\8*

Cardio & Blood