Cell Transformation (IMAGE) Penn State Caption Heart progenitors cells derived from human stem cells can be further specified to heart cells belong to external layer or muscle layer of a human heart. Credit Lance Lian, Penn State Usage Restrictions non commercial usage only License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.