In vivo tracking of individual sarcomeres along myofibrils in an LV myocyte of a mouse with high ΔLVP. (A) Confocal image of a myocyte expressing α-actinin-AcGFP. ΔLVP, 135.7 ± 1.5 mm Hg; HR, 496 ± 0.4 bpm. Within the yellow-outlined rectangles, five, six, and five sequentially connected sarcomeres were analyzed for M1, M2, and M3, respectively. Numbers indicate longitudinal positions of sarcomeres. Left and right arrowheads indicate sarcomere nos. 1 and 5 (or 6), respectively. Scale bar, 10 µm. See Video 7. (B) Triangular heat maps showing correlation between average and individual SLs (top row) and between an individual sarcomere and other sarcomeres in M1 (left), M2 (middle), and M3 (right; second row and below). (C) Color diagram showing CI between average and individual SLs during seven cardiac cycles for M1 (left), M2 (middle), and M3 (right). Cardiac cycle numbers are shown on left. Sarcomere numbers, same as in B. Bottom: Average of seven 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]).