Cardiomyopathies are mostly determined by genetic mutations affecting either cardiac muscle cell structure or function. Nevertheless, cardiomyopathies may also be part of complex clinical phenotypes in the spectrum of neuromuscular (NMD) or mitochondrial diseases (MD). The aim of this study is to describe the clinical, molecular, and histological characteristics of a consecutive cohort of patients with cardiomyopathy associated with NMDs or MDs referred to a tertiary cardiomyopathy clinic. Consecutive patients with a definitive diagnosis of NMDs and MDs presenting with a cardiomyopathy phenotype were described. Seven patients were identified: two patients with ACAD9 deficiency (Patient 1carried the c.1240C>T (p.Arg414Cys) homozygous variant inACAD9;Patient 2carried the c.1240C>T (p.Arg414Cys) and the c.1646G>A (p.Ar549Gln) variants inACAD9); two patients withMYH7-related myopathy (Patient 3carried the c.1325G>A (p.Arg442His) variant inMYH7;Patient 4carried the c.1357C>T (p.Arg453Cys) variant inMYH7); one patient with desminopathy (Patient 5carried the c.46C>T (p.Arg16Cys) variant inDES); two patients with mitochondrial myopathy (Patient 6carried the m.3243A>G variant inMT-TL1;Patient 7carried the c.253G>A (p.Gly85Arg) and the c.1055C>T (p.Thr352Met) variants inMTO1). All patients underwent a comprehensive cardiovascular and neuromuscular evaluation, including muscle biopsy and genetic testing. This study described the clinical phenotype of rare NMDs and MDs presenting as cardiomyopathies. A multidisciplinary evaluation, combined with genetic testing, plays a main role in the diagnosis of these rare diseases, and provides information about clinical expectations, and guides management.