## 2 Materials and Methods
### Statistical Analysis  
Statistical analyses were conducted by utilizing GraphPad Prism software version 7.0e (GraphPad Software Inc., Boston, CA, USA). Detailed information regarding the statistical methods employed and the sample sizes assessed can be found in the respective figure legends. In short, the data represented in Figure 1D,E were analyzed using one-way ANOVA followed by [PERSON]'s multiple comparison tests. The data represented in Figure 2C-F were analyzed using multiple \(t\)-test analyses to determine the statistical differences between untreated and NE-stimulated cells at each time point using the two-stage step-up method of [PERSON], [PERSON], [PERSON], with FDR set at 1%.  
Figure 1: Quantification of cardiomyocyte optical volumes in response to 24 h stimulation with 10 μM norepinephrine. (**A**) Overview of experimental design. Cardiac cultures derived from the hearts of postnatal day 1 (P1) to P3 rat pups cultured with and without 10 μM norepinephrine (NE) treatment and then visualized for 24 h on the Holomonitor M4 digital holographic imaging microscope. (**B**) Representative three-dimensional reconstructions of cultured cardiomyocytes (CM) and non-cardiomyocytes (non-CM) as visualized on the Holomonitor M4 at the beginning of our time-lapse imaging experiments at 0 h (0 hours). CMs were identified based on their larger size and overall thickness. (**C**) Representative three-dimensional reconstructions of cultured CMs untreated or stimulated with 10 μM NE at the end of our time-lapse imaging experiments (24 h). NE-treated CMs exhibited dramatic changes in morphology including spreading and the development of protrusions. (**D**) Measured optical volumes of untreated (\(n=256\)) and NE-stimulated (\(n=187\)) CMs at 0 h and 24 h of live-imaging on the Holomonitor M4 quantified from 4 independent cardiac cultures derived from P1-P3 rat hearts. (**E**) Measured optical volumes of untreated (\(n=140\)) and NE-stimulated (\(n=90\)) non-CMs at 0 and 24 h of live-imaging on the Holomonitor M4 quantified from 3 independent cardiac cultures derived from P1-P3 rat hearts. Values are reported as mean \(\pm\) standard deviation. One-way ANOVA, [PERSON]’s multiple comparisons test; \({}^{***}\), \(p<0.0001\); NS, not significant.  
Figure 2: Single–cell tracking of cardiomyocyte-surface area and optical volume dynamics during 24 h treatment with 10 mM norepinephrine. (**A**) Representative panels of three-dimensional reconstructions of cultured cardiomyocytes-c (CM) untreated or stimulated with 10 mM norepinephrine (NE) over 24 h of live imaging. (**B**) Representative panels depicting image segmentation and identification  
of well-isolated CMs using the HOLOMONITOR App Suite software and the Single Cell Tracking module. Drastic changes in cell volumes are flagged by the software (yellow triangles containing exclamation points) to assist with the validity of cell identification tracking. Raw surface area (**C**) and optical volume (**D**) dynamics of untreated (\(n\) = 256) and NE-stimulated (\(n\) = 187) cells over the course of 24 h imaging. Normalized surface area (**E**) and optical volume (**F**) dynamics were determined by dividing the value obtained at each time point by the initial value measured in cells at the start of the imaging experiment (0 h). Cellular measurements are pooled from the analysis of cultures from 4 independent cardiac culture preparations from P1-P3 rat hearts. Multiple \(t\)-test analysis was performed to determine statistical difference between untreated and NE-stimulated cells at each time point using the two-stage step-up method of [PERSON], [PERSON], and [PERSON] with FDR set at 1%: *, \(p\) < 0.05; **, \(p\) < 0.01; ***, \(p\) < 0.0001; NS, not significant.