An improvement to the GiWi protocol for differentiating human pluripotent cells to developmentally mature cardiomyocytes includes a step of activating innate immunity in mesoderm stage cells in the in vitro differentiation culture. When the mesoderm cells, which are precursors to cardiac progenitor cells, are primed by exposure to an activator of innate immunity, a population of cardiomyocytes is generated that is more developmentally mature than is generated in the GiWi protocol without the primed step. Also provided herein are in vitro ventricular conductive microtissues and isolated, in vitro populations of ventricular conduction system-like cells and methods for making the same.