Acute myocardial infarction (AMI) is one of the most significant causes of 
morbidity and mortality worldwide. Stem cells represent an enormous chance to 
rebuild damaged heart tissue. Correct definition of the cardiac progenitors is 
necessary to understand heart development, and would pave the way for the use of 
cardiac progenitors in the treatment of heart disease. Identifying, purifying 
and differentiating native cardiac progenitor cells are indispensable if we are 
to overcome congenital and adult cardiac diseases. To understand their 
functions, physiology and action, cells are tested in animal models, and then in 
clinical trials. But because clinical trials yield variable results, questions 
about proper cardiac stem cells remain unanswered. Transplanted stem cells 
release soluble factors, acting in a paracrine fashion, which contributes to 
cardiac regeneration. Cytokines and growth factors have cytoprotective and 
neovascularizing functions, and may activate resident cardiac stem cells. 
Understanding all these mechanisms is crucial to overcoming heart diseases.