Some forms are self-exciting and can spread excitation from cell to cell in a direct fashion. Other forms require neural stimulation to contract. Cardiac Muscle is a specialized form of striated muscle. The cells are very small and divided. Excitation can spread from cell to cell and any cell can potentially become self-exciting, if left alone long enough.
Cells have a very large proportion of their volume devoted to mitochondria.
This makes the contractions weaker than comparable amounts of skeletal muscle, but far more aerobic.