Briefly, cardiomyocytes were differentiated as previously described 10 (link). Cells were re-plated on BD matrigel-coated glass bottom dishes as single cells. Cellular actin was labeled with Life Technologies CellLight® Actin-RFP (BacMam 2.0). Imaging was performed on a Nikon A1R confocal using a Nikon CFI Plan Apo VC 60X water immersion objective, and cells were maintained at 37°C using a Tokai Hit Stagetop Incubator. Cardiomyocytes were identified by rhythmic beating. A region of sarcomere was bleached using a 561nm laser at 100% power, and recovery of fluorescence was measured every second for 60 seconds, followed by every 8 seconds until 10 minutes after bleaching. The size of the bleaching area was identical for all experiments. Fluorescence recovery was calculated using pre-bleach fluorescence intensity in the bleached area. Statistics were performed using Graphpad’s Prism software.