Animal studies can be poor predictors of human drug response. Species-specificity of organs is a concern especially for the heart. Many drugs that enter clinical trials will fail ultimately because of unexpected cardiotoxicity. Drug developers would love to mitigate such risks through in vitro human cardiac testing, but human heart biopsy materials and donor organs do not survive well in a laboratory setting. Breakthroughs with human stem cells offer an alternative. It is now possible to take a simple skin…