Synchrotron X-ray Phase Contrast micro-tomography, as implemented at the TOMCAT beamline (PSI), provide essential and unique 3D reconstructions of complete hearts (see figure) for understanding cardiac microstructure and its influencing factors, both on small animals or human fetal hearts. The aim of our current Heart Imaging Project is to quantify cardiac structures and tissues for the first time at micrometre scale, non-destructively, without the use of contrast agents and in 3D.