Verified Answer :

A myocardiocyte is a heart muscle cell, but it makes up the myocardium
Cells > Tissues > Organs > Organ System > Organism
We know it's more than a cell but less than an organ, because a heart muscle is found in the heart (an organ).
Therefore, it's a type of tissue.

The correct answer is Tissue.

The myocardiocyte is a heart muscle cell and cells combine to form tissue, tissues helps in the formation of  organ and organs combine to form organ system.

This organ system makes the human body.

This is a connective tissue found in the heart. Heart is divided into Three layers epicardium, mayocardium (muscular layer) and endocardium.