<prompt> Contractility of cardiac muscle depends onOn T tubulesOn T tubules and extracellular Ca2On extracellular Ca2On intracellular Ca2  <response>: Excitation and contraction coupling is there in cardiac muscle. When an action potential reaches the T tubules there is activation of Dihydropyridine channels. This causes influx of extracellular calcium into sarcoplasm. Ref: Textbook of medical physiology by N Geetha, 2nd edition, page no. 53 