Fig. 1. The method of heart rate analysis using high speed video imaging. For analysis of the short-term heart rate variability (HRV) images (frames) of the beating heart were taken with 1000 or 200 frames s^–1 and stored on the frame grabber's on-board memory. One sample image is shown in (A). Dotted lines indicate the perimeter of the atrium (a) and the ventricle (v). For each image a line was drawn beginning outside the heart tissue, cross sectioning the centre of ventricle and atrium and ending in the sinus venosus (solid line). Luminance profiles along these lines (see B), were stored for all frames. The intersection of the red lines marks the point on the line, where grey values through all frames are compiled to a luminance periodogram (C). The detected peaks (blue squares in C) were used for the calculation of inter-beat frequency (Hz) and plotted against frames in the tachogram (D). Red circles are the unfiltered raw data of every individual beat, and black rectangles represent the median filtered signal (median ranking=10). These data were taken for further analysis.