The classical Cepheid Leavitt Law (Period-Luminosity relation) has been known for 100 years, and used as in extragalactic distance determination for nearly as long. However, Cepheids still present us with surprises. Recent results about X-ray behavior is just one example. Around minimum radius the pulsation wave from the envelope creates a disruption in the photosphere and chromosphere. X-ray activity, on the other hand remains constant at a low level at this phase. Just after maximum radius, however, X-ray flux increases sharply (four fold in the case of δ Cep). We summarize here the observational program to explore parameters involved and theoretical investigations searching for a basic understanding of this upper atmosphere phenomena.