A number of calcium-activated nonselective cation (NSC(Ca)) currents recorded from cardiac preparations have been described in the literature. These currents are implicated in membrane depolarization and in the modulation of cardiac activity. The discovery of a novel family of cation channels, the "transient receptor potential" (TRP) protein family, has revived interest in the study of nonselective cation channels. In particular, the TRPM4 protein provides the basis for an NSC(Ca) channel detected in heart preparations. The role of this channel should not be neglected in the description of our understanding of heart activity and the development of arrhythmias induced by calcium waves. This review focuses on the electrophysiologic and regulatory properties of this native NSC(Ca) channel in cardiac preparations compared with those of the TRPM4 protein. Physiologic and pathologic implications of the current carried by this channel are discussed.