At the intracellular level, hECTs exhibit several essential structural features of cardiomyocytes, including organized sarcomeres, gap-junctions, and sarcoplasmic reticulum structures; however, the distribution and organization of many of these structures is characteristic of neonatal heart tissue rather than adult human heart muscle.  hECTs also express key cardiac genes (α-MHC, SERCA2a  and ACTC1) nearing the levels seen in the adult heart. Analogous to the characteristics of ECTs from animal models, hECTs beat spontaneously  and reconstitute many fundamental physiological responses of normal heart muscle, such as the Frank-Starling mechanism and sensitivity to calcium. hECTs show dose-dependent responses to certain drugs, such as morphological changes in action potentials due to ion channel blockers  and modulation of contractile properties by inotropic and lusitropic agents.