The contractile activity of the heart depends on the coordinated activation of cardiac muscle cells, as well as the activation of each region within these cells. The conversion of an electrical signal into a mechanical process is known as excitation-contraction coupling; this process depends on the accurate organization and functional coupling between the different participating structures. The T-tubules and the sarcoplasmic reticulum constitute the dyads, a functional structure where the activity of voltage-gated calcium channels is coupled with the type 2 ryanodine receptor to generate calcium-induced calcium release. This phenomenon increases the intracellular calcium concentration, allowing cell contraction. The relaxation process occurs at the same time as calcium extrusion or recapture into the sarcoplasmic reticulum. The formation of the T tubules, the organization of the dyad, and the distribution of the proteins that regulate the entry, reuptake, and extrusion of calcium involve different structural proteins whose expression, localization, and function can be affected in pathological processes such as heart failure. In this chapter, we give an overview of the proteins involved in cardiac cell ultrastructural organization and an insight into changes and possible causes of these changes found in diabetes, obesity, and heart failure models.