Because the myocardium depends heavily on oxidative metabolism, it is not surprising that genetic errors of mitochondrial function often result in cardiomyopathies. The emphasis of this review is on disorders of the respiratory chain, the only area of cell metabolism that is under dual genetic control: 1) the mitochondrial genome (mtDNA) encodes 13 subunits of respiratory chain complexes, and 2) the nuclear genome not only encodes all other respiratory chain proteins, but also mitochondrial translocases, components of the mitochondrial protein transport machinery, and factors that are essential for mtDNA transcription, translation, and replication. Mitochondrial cardiomyopathies due to mutations in the nuclear DNA are inherited as mendelian traits involving structural or enzyme proteins of the respiratory chain, mitochondrial protein importation, or the dialogue between the two genomes. Mitochondrial cardiomyopathies due to mtDNA mutations can be sporadic or inherited as maternal traits and follow the rules of "mitochondrial genetics," which are outlined briefly. MtDNA mutations can cause isolated cardiomyopathies or, more often, multisystem disorders of which cardiac involvement is a major component. We review recent advances in this rapidly expanding field and briefly discuss pathogenetic problems and the mitochondrial theory of presbycardia.