Heart failure is a serious and often fatal medical condition caused by inability of heart to pump enough blood around the body. It is one of the leading causes of death in ageing population. One of the core causes behind heart failure is the inability of adult mammalian heart to regenerate heart muscle cells or cardiomyocytes after they are lost due to other health conditions. Remarkably, human cardiomyocytes can divide in foetal state but lose their ability to regenerate soon after birth. In sharp contrast, heart regeneration is common in non-mammalian vertebrates such as zebrafish. Remarkably, adult zebrafish can regenerate its heart after loss of as much as 20% of its ventricle. Understanding how cardiomyocytes divide is a key to the treatment of heart diseases. In addition, finding means of boosting cardiomyocyte proliferation will help in culturing them longer in laboratory, improving models of heart function and understanding pathology of heart diseases.