Background/Purpose: Left ventricular hypertrophy is a major cause of heart failure in aging population. This study is to determine whether an excess dietary fat is lipotoxic or lipoprotein to the hypertrophic aging heart. Methods: At 44-week-old, a normal chow (12% fat) was replaced a high-fat diet (HFD; 45% fat) for randomly selective spontaneously hypertensive rats (SHR + HFD, n = 6) and Wistar-Kyoto rats (WKY + HFD, n = 6, normotensive control). Others (SHR, n = 11; WKY, n = 10) were continuously fed with normal diets. After 27 weeks, electrocardiogram, echocardiography, and femoral arterial catheterization were performed before rats being sacrificed for molecular biology analyses. Results: HFD aggravated cardiac atrial, ventricular dilation and hypertrophy in SHR (LV mass: SHR + HFD 2026.0 ± 424.9 vs SHR 1449 ± 461.1 mg, unpaired t test P < 0.05). HFD caused significant atrial dilatation in both WKY (LA diameter, 5.38 ± 0.36 vs 4.11 ± 0.42 mm, P < 0.001) and SHR (6.13 ± 0.79 vs 4.69 ± 1.00, P < 0.01). Only in SHR, HFD induced significant left ventricular dilatation (LV diameter, 8.87 ± 1.25 vs 7.08 ± 1.00 mm, P < 0.01) and reduced ejection fraction (LVEF, 62.8 ± 11.6 vs 75.1 ± 9.2 mm, P < 0.05). The α-myosin heavy chain was significantly upregulated in atria and ventricles of HFD groups. HFD induced significant upregulation of PPARα, ACADM, and TNFα transcripts in atrial tissues (P < 0.05). Conclusion: Hypertensive heart disease in aging rats was aggravated by HFD with worse atrial, ventricular remodeling and associated with left ventricular systolic function impairment. Keywords: SHR, High-fat diet, Hypertension, Hypertensive heart disease, Heart failure, Remodeling