Figure 2.

Schematic illustration shows the protocol to estimate the prestrains of the epicardial layer on the unpressurized intact heart. (a) By putting four squarely-arranged markers on the epicardial surface of the unpressurized intact heart, we could obtain the in situ marker dimensions while the prestrains existed. After dissecting the same region off the heart, the marker dimensions of the stress-free epicardial layer could be measured for the calculation of the prestrains. (b) Markers tagged from ImageJ for in situ unpressurized intact heart (left panel) and stress-free epicardial sample (right panel). The ruler with actual size was printed on a paper. The paper ruler could be placed onto the left ventricle surface, perfectly fitting the curvature of the left ventricle surface (left panel). In this way, the readings of the real marker dimensions on the unpressurized intact heart can be accurate, without being skewed by using a straight ruler for a curved surface. By immersing the isolated epicardial layer in the 1X PBS in a Petri dish, we obtained the new marker dimension of the epicardial layer under stress-free status (right panel). Ruler with actual size was printed on the transparent film and then placed beside the stress-free epicardial layer sample (right panel). (c) Sample dissection plan for estimating prestrains of the epicardial layer on the unpressurized intact heart. (Online version in colour.)