Adenosine Triphosphate, Analysis of Variance, Animals, Cardiomegaly, Energy Metabolism, In Vitro Techniques, Lactates, Magnetic Resonance Spectroscopy, Male, Myocardial Ischemia, Perfusion, Phosphocreatine, Phosphorus Isotopes, Rats, Rats, Sprague-Dawley, Sodium, Sodium Isotopes, Time Factors, Ventricular Fibrillation