Myocardium (cardiac muscle tissue) must rhythmically contract for a lifetime. This requires considerable amount of energy production by the cells. You would expect to see relatively high of?

The correct answer is mitochondria.

The mitochondria are the organelles that are responsible for the production of energy in the cells. Since the myocardium (cardiac muscle tissue) must rhythmically contract for a lifetime and this requires a considerable amount of energy production, it would be expected that there would be a relatively high number of mitochondria in these cells.