Researchers find a low-cost way of creating cardiomyocytes on demand: they can "transform human stem cells - both embryonic and induced pluripotent stem cells - into the critical heart muscle cells by simple manipulation of one key developmental pathway. ... manipulating a major signaling pathway known as Wnt - turning it on and off at prescribed points in time using just two off-the-shelf small molecule chemicals - is enough to efficiently direct stem cell differentiation to cardiomyocytes. ... The technique promises a uniform, inexpensive and far more efficient alternative to the complex bath of serum or growth factors now used to nudge blank slate stem cells to become specialized heart cells. ... Our protocol is more efficient and robust. We have been able to reliably generate greater than 80 percent cardiomyocytes in the final population while other methods produce about 30 percent cardiomyocytes with high batch-to-batch variability. ... The ability to make the key heart cells in abundance and in a precisely defined way is important because it shows the potential to make the production of large, uniform batches of cardiomyocytes routine. [The] cells are in great demand for research, and increasingly for the high throughput screens used by the pharmaceutical industry to test drugs and potential drugs for toxic effects. ... Scientists also have high hopes that one day healthy lab-grown heart cells can be used to replace the cardiomyocytes that die as a result of heart disease. ... Many forms of heart disease are due to the loss or death of functioning cardiomyocytes, so strategies to replace heart cells in the diseased heart continue to be of interest. For example, in a large heart attack up to 1 billion cardiomyocytes die. The heart has a limited ability to repair itself, so being able to supply large numbers of potentially patient-matched cardiomyocytes could help."