WHY DOES THE HEART NOT GET TIRED?

In a person's lifetime, a human heart can contract billions of times.

The heart is still a muscle, much like the bicep or the hamstring, but the heart never tires. 

The reason for this rather crucial detail of anatomy keeps us alive, as without a pumping heart death will shortly follow. 

Hearts, although muscles, are made up of different fibres than their counterparts.

This type of fibre, known as cardiac tissue, only exists in the heart and nowhere else in the human body. 

Skeletal muscle tires quickly, and can switch from aerobic respiration to anaerobic respiration - producing lactic acid which causes cramp.

If this was to happen in the heart it would cause a heart attack.

To avoid this happening and to allow for constant use without fatigue, the cardiac tissue has a different arrangement.

Cardiac tissue has far more mitochondria which produces a huge amount more energy in the form of a chemical called Adenosine Triphosphate (ATP).

Mitochondria are small organelles within cells which are considered to be the powerhouse of the cell and convert glucose into energy inside the organelle. 

Having more of these means the heart as an organ will never run out of energy under normal circumstances. 

The reason this arrangement does not occur in all muscle sis the energy requirements would be enormous, and unsustainable. 

The human body would simply demand more energy than it can create.