In vivo analysis of individual T-tubular distances in an LV myocyte of a mouse. (A) Confocal image of a CellMask-treated LV myocyte in a heart of a mouse. ΔLVP, 73.0 ± 0.3 mm Hg; HR, 492 ± 0.4 bpm. In three myofibrils, five sequentially connected T-tubular distances (within yellow-outlined rectangles) were analyzed (M1, M2, and M3). Arrowheads indicate T-tubule nos. 1 and 5, respectively. Scale bar, 10 µm. See Video 6. (B) Triangular heat maps showing correlation between average and individual T-tubular distance (top row) and between an individual T-tubular distance and others in M1 (left), M2 (middle), and M3 (right; second row and below). Numbers for T-tubular distances are indicated on top and left of each row. (C) Color diagram showing CI between average and individual T-tubular distances during six cardiac cycles for M1 (left), M2 (middle), and M3 (right). Cardiac cycle numbers are shown on left. Numbers for T-tubular distances, same as in B. Bottom: Average of six cycles (i.e., same as top row in B) for each myofibril. In B and C, CI is shown based on a color scale (i.e., from 1 [dark blue] to −1 [dark red]).