Human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes are a novel source of cells for patient-specific cardiotoxicity drug testing, drug discovery, disease modeling, and regenerative medicine. We describe a versatile and cost-effective protocol for in vitro cardiac differentiation that is effective for a wide variety of hiPSC and human embryonic stem cell (hESC) lines. This highly optimized protocol produces contracting human embryoid bodies (hEB) with a near total efficiency of 94.7  �  2.4% in less than 9 days, and minimizes the variability in cardiac differentiation commonly observed between various hiPSC and hESC lines. The contracting hEB derived using these methods contain high percentages of pure functional cardiomyocytes, highly reproducible electrophysiological profiles, and pharmacologic responsiveness to known cardioactive drugs.