Introduction: Primary carnitine deficiency (PCD) is a rare autosomal recessive disorder caused by loss of function mutations in the solute carrier family 22 member 5 (SLC22A5) gene that encodes a high-affinity sodium-ion-dependent organic cation transporter protein (OCTN2). Carnitine deficiency can result in acute metabolic decompensation or, in a more insidious presentation, cardiomyopathy. Cardiomyopathy associated with PCD often presents with life-threatening heart failure. This presentation also usually includes skeletal muscle myopathy. Early recognition of this disorder and treatment with carnitine can avoid life-threatening complications related to cardiomyopathy. Case Presentation: Herein, we present a 10-month-old male patient with PCD, which was diagnosed while investigating the etiology of dilated cardiomyopathy and confirmed by molecular genetic analysis. Conclusion: Homozygous c.254_265 insGGCTCGCCACC (p.I89Gfs) pathogenic variant of the SLC22A5 gene was detected. With oral L-carnitine supplementation, the free carnitine level increased up to 14 μmol/L and the symptoms disappeared. LVEF increased by 45–70%. We would like to emphasize that this problem is a combination of the metabolic decompensation and the cardiac phenotypes, which are usually separated to either phenotype.