The mitochondrial enzyme monoamine oxidase A (MAO-A) is widely distributed in neuronal, myocyte and non-myocyte cardiac compartments. After the demonstrations that both cardiac neuronal and extraneuronal MAO-A contribute to the degradation of norepinephrine and serotonin, several studies attempted to determine the impact of MAO-A activity in the control of local concentration of the two biogenic amines and in their receptor-mediated effects. From the 2000s, an additional mechanism of action of MAO-A has been proposed. Such mechanism involves hydrogen peroxide (H2O2) production during substrate degradation. This finding stimulated a growing interest on the role of MAO-A-dependent oxidative stress in cardiac pathophysiology. Altogether, the results obtained by different groups showed that MAO-A played a key role in the regulation of physiological cardiac function and in the development of acute and chronic heart diseases through two mechanisms: the regulation of substrate concentrations and the intracellular production of reactive oxygen species. In this review, we will give an overview of the major results on the role of MAO-A in the field of cardiac diseases.