A 29-week-old male foetus was diagnosed by foetal echocardiography with severe hypertrophic cardiomyopathy with systolic dysfunction and generalized oedema, undergoing a Caesarean section at 33 weeks. Mechanical ventilation and milrinone infusion were required during the first week. Systolic function and output parameters improved progressively. Metabolic and infectious screenings were negative. At the follow-up, during the first year of life, hypertrophy regressed, posterior right auricular hypertrophy evolved to a mass with cysts, and left ventricular myocardium developed trabeculations accomplishing non-compaction criteria. Recently, mutations in genes previously implicated in the pathogenesis of hypertrophic cardiomyopathy have been identified in patients with left ventricular non-compaction without hypertrophy. This report suggests that these cardiomyopathies may have a similar genetic origin, and can co-exist in the same patient.