“Alternans” is an arrhythmia exhibiting alternating amplitude or alternating interval from heartbeat to heartbeat, which was first described in 1872 by Traube. Recently alternans was finally recognized as the harbinger of a cardiac disease because physicians noticed that an ischemic heart exhibits alternans. To quantify irregularity of the heartbeat including alternans, we used the detrended fluctuation analysis (DFA). We revealed that in both, animal models and humans, the alternans rhythm lowers the scaling exponent. This correspondence describes that the scaling exponent calculated by the DFA reflects a risk for the “failing” heart.