ACKNOWLEDGEMENTS
The authors are indebted to all those families who permitted the hearts of their children to be included in the archive. They thank Clinical Photography at the Birmingham Women’s and Children’s NHS Foundation Trust for making the original images of selected hearts from the archive (Figures 1, 2, 6 and 7 and the central image) for which they retain the copyright.

Funding
N.E.D is supported by an Intermediate Clinical Research Fellowship from the British Heart Foundation [FS/15/49/31612]. No specific funding was received for this study.
Conflict of interest: none declared.