Some facts about human heart -- Did you know?

1. The heart is a cone-shaped structure which lies in the middle of the chest, slightly to the left, behind the breastbone and between the lungs.

2. The heart of a healthy 70 kg adult pumps about 7,200 litres of blood daily at a rate of approximately 5 litres per minute.

3. The heart is enclosed in a sac called the pericardium. The wall of the heart is made up of three layers known as the epicardium (outer layer), myocardium (middle layer), and endocardium (inner layer) respectively. The epicardium and endocardium are thin protective layers. In contrast, the myocardium is a thick, muscular layer which provides the strength for the heart to function as a pump.

4. The average heart rate is roughly 72 beats per minute, which translates into approximately 100,000 beats per day. This figure may, however, differ widely among people of different age groups. For instance, the heart rate may be as high as 120 beats per minute in infants, and as low as 60 beats per minute in adults.

5. The average adult human heart is about the size of a clenched fist and weighs about 300 g.

6. The characteristic “lub-dub” of a heartbeat is caused by the movement of the heart valves during each cardiac cycle. In the first phase, which is known as the systole, the tricuspid andmitral valves close, producing the “lub” sound. In the second phase (the diastole), the pulmonary and aortic valves close, resulting in the “dub” sound.

Information Source: http://www.myheart.org.sg/?page_id=38