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We have used accelerometers to measure the heart's motion. A 3-axis sensor prototype was made from two commercially available accelerometers, and tested on anesthetized pigs. The chest wall of the pig was opened, the sensor sutured to the heart, and motion data was recorded over several hours. The heart's own beating is partly concealed by other sources of motion, particularly the respiration. High-pass filtering was used to isolate the heart beating from these other motions. The filter cut-off frequency was set to 1.0 Hz, including the heart rate at 1.5 Hz, while suppressing the respiration at 0.3 Hz. Velocity and position were obtained by numerically integrating the filtered acceleration traces. Using this procedure, the heart motion could be measured in great detail. Motion abnormalities, e.g. arrhythmias and fibrillation, were identified in the motion curves, and confirmed by comparison with synchronously recorded ECG data.