Which of the following is the source of energy for a cardiac muscle at normal conditions?

Hea consumes more energy than any other organ. It utilizes about 6 kg of ATP per day, 20-30 times of its own weight. Cardiac muscle derives its energy by oxidative metabolism of fatty acids (60-90%) and glucose 10-40%. Ketone bodies are also normally metabolized. In addition, energy transfer to hea's myofibrils occurs by creatine kinase catalyzed energy shuttle. The metabolism of hyperophied hea switches from fatty acid to glucose. Ref: Textbook of Biochemistry for Medical Students By D. M. Vasudevan, Sreekumari S, Kannan Vaidyanathan, 2013, Page 102.