Final answer:
Muscle cells in the mammalian heart are multinucleate due to the fusion of myoblast cells, which is different from skeletal muscle cells. The presence of multiple nuclei affects the cell cycle in a muscle cell.
Step-by-step explanation:
Muscle cells in the mammalian heart are multinucleate because they are formed from the fusion of many smaller myoblast cells. This means that instead of having a single nucleus, these muscle cells contain multiple nuclei within a continuous cytoplasm. In contrast, skeletal muscle cells are also multinucleate but because each contributing myoblast cell retains its nucleus in the mature muscle cell. The cell cycle in a muscle cell is different because the large number of nuclei present affects processes such as DNA replication and cell division.