How does this level of organization relate to cells? To organ systems?

The heart —belonging to the organ level of organization— is composed of cardiac muscle cells forming the myocardium, and belongs to the cardiovascular system.

Explanation:

The cellular level of organization of the heart is complex, since it is a group of specialized cells that constitute the main organ of the cardiovascular system.

The heart is predominantly made up of the myocardium, formed by muscle cells similar to those of the striated muscle, but with a different distribution. Other cells belonging to the heart are the endothelial cells, which cover its interior, and the fibrous and serous cells that constitute the pericardium.

Structurally, the heart is part of the cardiovascular system, whose function is to carry blood throughout the body. Functionally, this organ is related to all the tissues, organs and systems of the body.

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