Implantable cardiac devices have very strict restrictions on energy dissipation since battery change requires surgery. Today the battery longevity of pacemakers during standard use is up to 10 years which might seem sufficient. However, new functionality is constantly being introduced requiring more advanced signal processing algorithms which in turn increase energy dissipation. New battery technologies are of course beneficial, but compared to the progress of electronics according to Moore's Law, battery development is very slow and energy issues have to be solved by more efficient implementations. Technology scaling will help us by reducing capacitance and thereby lowering the dynamic energy. However, for technology nodes of 130 nm and below static energy dissipation due to leakage currents, which traditionally could be ignored, are becoming increasingly important. This is especially true for low sampling rate applications were the dynamic energy often may be ignored. In this paper we will make an introduction to the topic, discuss the mechanisms of energy dissipation and present some specific solutions regarding implementation of signal processing in implantable cardiac devices. Special attention will be given to reduced leakage and a dual mode operation.