Niemann-Pick disease type B (NPD-B) is a rare lysosomal storage disorder caused by biallelic mutations in the SMPD1 gene, leading to deficient acid sphingomyelinase activity and lipid accumulation in various organs. Although cardiac involvement is known in similar disorders like Anderson-Fabry disease, the myocardial impact in NPD-B remains poorly characterized. Two adult patients with genetically confirmed NPD-B underwent multiparametric cardiac magnetic resonance (CMR) including native T1 mapping and late gadolinium enhancement (LGE). Clinical, biochemical, and histopathological data were reviewed. Patient 1, a 59-year-old man with a homozygous SMPD1 mutation (c.[Arg610del]), showed advanced pulmonary disease and liver steatosis. CMR revealed biventricular dilation with preserved systolic function and reduced native T1 values without LGE, suggesting myocardial lipid accumulation. Despite enzyme replacement therapy, the patient died of pulmonary complications 22 months later.Patient 2, a 31-year-old woman with compound heterozygous SMPD1 mutations (c.[739G > A], c.[1801G > A]), had cirrhosis, dyslipidemia, and stable lung disease. CMR showed normal T1 values and no cardiac abnormalities. This study compares two adult NPD-B patients who underwent CMR imaging. The first patient who died during follow-up showed reduced native T1 values, suggesting myocardial lipid accumulation, while the second had normal values and no complications during follow-up. These two patients are reported here to stimulate research in this field, as native T1 may aid in assessment of myocardial involvement. The two cases also suggest a potential influence of genetic mutations on disease severity. Given the risk of cardiac involvement in NPD-B, CMR - especially T1 mapping - may be a valuable tool for assessing myocardial infiltration. Future studies are needed to explore its correlation with genotype, disease progression, and treatment response.