Myocardial metabolic and perfusion imaging is a vital tool for understanding the physiologic consequences of heart failure. We used PET imaging to examine the longitudinal kinetics of ¹⁸F-FDG and 14(R,S)-¹⁸F-fluoro-6-thia-heptadecanoic acid (¹⁸F-FTHA) as analogs of glucose and fatty acid (FA) to quantify metabolic substrate shifts with the spontaneously hypertensive rat (SHR) as a model of left ventricular hypertrophy (LVH) and failure. Myocardial perfusion and left ventricular function were also investigated using a newly developed radiotracer ¹⁸F-fluorodihydrorotenol (¹⁸F-FDHROL). Longitudinal dynamic electrocardiogram-gated small-animal PET/CT studies were performed with 8 SHR and 8 normotensive Wistar-Kyoto (WKY) rats over their life cycle. We determined the myocardial influx rate constant for ¹⁸F-FDG and ¹⁸F-FTHA (K_i^FDG and K_i^FTHA, respectively) and the wash-in rate constant for ¹⁸F-FDHROL (K₁^FDHROL). ¹⁸F-FDHROL data were also used to quantify left ventricular ejection fraction (LVEF) and end-diastolic volume (EDV). Blood samples were drawn to independently measure plasma concentrations of glucose, insulin, and free fatty acids (FFAs). K_i^FDG and K_i^FTHA were higher in SHRs than WKY rats (P < 3 × 10⁻⁸ and 0.005, respectively) independent of age. A decrease in K_i^FDG with age was evident when models were combined (P = 0.034). The SHR exhibited higher K₁^FDHROL (P < 5 × 10⁻⁶) than the control, with no age-dependent trends in either model (P = 0.058). Glucose plasma concentrations were lower in SHRs than controls (P < 6 × 10⁻¹²), with an age-dependent rise for WKY rats (P < 2 × 10⁻⁵). Insulin plasma concentrations were higher in SHRs than controls (P < 3 × 10⁻³), with an age-dependent decrease when models were combined (P = 0.046). FFA levels were similar between models (P = 0.374), but an increase with age was evident only in SHR (P < 7 × 10⁻⁶). The SHR exhibited alterations in myocardial substrate use at 8 mo characterized by increased glucose and FA utilizations. At 20 mo, the SHR had LVH characterized by decreased LVEF and increased EDV, while simultaneously sustaining higher glucose and similar FA utilizations (compared with WKY rats), which indicates maladaptation of energy substrates in the failing heart. Elevated K₁^FDHROL in the SHR may reflect elevated oxygen consumption and decreased capillary density in the hypertrophied heart. From our findings, metabolic changes appear to precede mechanical changes of LVH progression in the SHR model.