All of the following are true about cardiac muscles, EXCEPT:

Mammalian heas have an abundant blood supply, numerous mitochondria, and a high content of myoglobin, a muscle pigment that can function as an O2 storage mechanism. Normally, less than 1% of the total energy liberated is provided by anaerobic metabolism. Ref: Ganong's Review of Medical Physiology 23rd edition, Chapter 5.