Introduction: Spectral CT can acquire effective atomic (EAN) and electron density number (EDN). Hypothesis: EAN and EDN using spectral CT enable the differentiation of infarcted myocardium and hypertrophied myocardium from normal myocardium. Methods: We analyzed 146 patients (73 males; mean age 55 ± 14 years old) who had no significant coronary stenosis on CT (7500; Philips) and normal ECG (normal group), 20 patients with previous myocardial infarction (MI) (12 males; mean age 73 ± 7 years old) (MI group), and 10 patients with hypertrophic cardiomyopathy (HCM) (5 males; mean age 66 ± 15 years old) (HCM group). On CT, we measured EAN and EDN in the interventricular septum (IVS), left ventricular (LV) anterior wall (LVAW), and lateral wall (LVLW) within a 1.0 mm2 circle at LV inflow level in the non-contrast and early contrast phase. In MI and HCM groups, EAN and EDN were also measured in the infarcted and hypertrophied myocardium, respectively. Results: In the non-contrast and early contrast phase, the EAN was significantly lower in the infarcted myocardium group than in the normal group (p < 0.01), in the non-infarcted myocardium than in the MI group (p < 0.05) and non-hypertrophied myocardium in the HCM group (p < 0.05), and in the hypertrophic myocardium in the HCM group than in the normal group (p < 0.05) and non-hypertrophic myocardium in the HCM group (p < 0.05). In the non-contrast and early contrast phase, the EDN was also lower in the infarcted myocardium than in the normal group (p < 0.01), non-infarcted myocardium in the MI group (p < 0.05), hypertrophied and non-hypertrophied myocardium in the HCM group (p < 0.05). Conclusion: The use of EAN and EDN enables the differentiation of infarcted myocardium (EAN and EDN) and hypertrophied myocardium (EAN) from normal myocardium even on non-contrast CT alone. The use of EAN and EDN enables the detection of abnormal myocardial characteristics (blood flow decrement, fibrotic change, hypertrophy, and inflammation) on non-contrast CT alone.