Fig. 1: Experimental design for chronic 4-hydroxytamoxifen treatment.

a Cells are replated on day 10 (D10), then seeded onto our bioengineered platform on day 25 (D25). Cells are imaged and treated every 3 days from day 30 (D30). b Schematic of iPSC-CMs cultured in a monolayer (left) and as single cells on extracellular matrix (ECM) micropatterns with a length to width aspect ratio of 7:1 (right). c Motion-tracking analysis was used to measure the beating rate and beating velocity of the iPSC-CM monolayers and single cells. Videos of contracting cardiomyocytes are recorded, and analysis is performed to calculate speed of contraction (d/dt). The beating rate is defined as the number of contraction cycles per unit of time. The beating velocity is defined as the maximum contraction speed. d Ratiometric analysis of calcium flux in iPSC-CM single cells. Videos of contracting cardiomyocytes loaded with a ratiometric calcium dye are recorded, and analysis is performed to measure calcium bound dye and calcium-free dye relative to baseline (ΔF/F₀). Time to peak is defined as the time between the local minimum at the start of the peak and the next local maximum. Transient amplitude is defined as the difference between the maximum ΔF/F₀ and the minimum ΔF/F₀ for each peak. Frequency is the number of calcium oscillations per second. The resting calcium ratio is the minimum ΔF/F₀. Peak calcium ratio is the maximum ΔF/F₀.