Evidence for an unfolded border-collision bifurcation in paced cardiac   tissue
  We investigate, both experimentally and theoretically, the bifurcation to alternans in heart tissue. Previously, this phenomenon has been modeled either as a smooth or as border-collision period-doubling bifurcation. Using a new experimental technique, we find a hybrid behavior: very close to the bifurcation point the dynamics are smooth-like, whereas further away they are border-collision-like. This behavior is captured by a new type of model, called an unfolded border-collision bifurcation. 
Carolyn M. Berger, Xiaopeng Zhao, David G. Schaeffer, Hana M.   Dobrovolny, Wanda Krassowska and Daniel J. Gauthier