When does the unborn child's heart begin to beat?

 At the 18th day from conception the heart starts to beat and by the 21st day its mechanism of pumping blood through a closed system has began.

How can I ensure that my cholesterol levels do not rise?

 Eat healthily i.e. eat foods low in salt and fat as these would lead to a rise in cholesterol levels.

The heart is said to be Myogenic. What does Myogenic indicate?

The heart is a myogenic organ that receives impulses originating from with in the muscles of the heart and not from any external sources.