The viability of the ischemic myocardium is jeopardized by alterations, such as ATP decrease and elevation in intracellular [Ca(2+)], that are related to derangements in mitochondrial function. Besides these established notions, the elucidation of the apoptotic cascade and the availability of novel methodologies for in situ studies prompted new interest in mitochondria. The characterization of mitochondrial channels provided a contribution that is particularly relevant to cardiovascular research. Here we focus on the role of the permeability transition pore by analyzing the methodological requirements for its characterization, the consequences of its opening and the possible relationships with other mitochondrial functions, especially with the K(ATP) channels.