The Heart: The heart is a tough, hollow muscle about the size of a fist that pumps blood. The heart is enclosed in a tough sack of tissue called the pericardium. The average human heart beats about 70 times a minute, and with each beat it pumps about 5 ounces of blood, or about 4,000 gallons of blood each day. The heart rests in between beats, so it works less than half the time and rests more than …showed first 75 words of 1369 total…

…showed last 75 words of 1369 total…can by-passes the lungs. This artery, called the ductus arteriosus, must close shortly after birth. If it does not, surgery may be required to close it so that old and oxygenated blood will not mix. An instrument called an electrocardiograph can detect and record the electrical activity of the heart. The record of the electrical activity of the heart is called an electrocardiogram or EKG. The EKG is often used to help diagnose heart disease.