["Clinical and Experimental Pharmacology and Physiology, Volume 53, Issue 5, May 2026. ", "\nABSTRACT\nViral infections are a major cause of cardiac metabolic dysfunction, leading to diseases like viral myocarditis and heart failure. In this study, we used G3‐YSD, a synthetic DNA mimic from the HIV‐1 genome, to model cytoplasmic viral DNA stress and aim to elucidate the mechanistic roles of TRMT13 and SPAST in cardiomyocyte metabolic impairment under conditions mimicking viral infection. Through functional assays such as ATP quantification and Seahorse XF metabolic stress tests on H9C2 and AC16 cells, we found that G3‐YSD treatment suppressed cardiomyocyte energy metabolism in a dose‐ and time‐dependent manner, with upregulation of TRMT13 and SPAST. Further analysis revealed a strong positive association between these two genes. Functional knockdown experiments showed that silencing TRMT13 or SPAST alleviated G3‐YSD‐induced energy metabolic impairment. Mechanistically, miR‐409‐3p was identified as a key intermediary directly targeting the 3′UTRs of TRMT13 and SPAST, with TRMT13 mRNA acting as a ceRNA to promote SPAST expression. In vivo validation using a G3‐YSD‐treated mouse model confirmed that knocking down TRMT13 or SPAST, or delivering miR‐409‐3p mimics, improved cardiac function and systemic metabolic activity, while SPAST overexpression negated these effects. Our study identifies a novel TRMT13–miR‐409‐3p–SPAST regulatory axis mediating cardiomyocyte energy metabolic decline in response to cytoplasmic viral DNA stress, revealing a nonmethyltransferase, nonimmune, ceRNA‐based mechanism of a newly characterised tRNA methyltransferase in viral infection‐induced cardiac metabolic dysfunction and proposing new molecular targets for therapeutic intervention.\n"]