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5 bytes added, 09:25, 14 May 2009
[[Image:Hart_cells_en.png|thumb|left|The heart consists of approximately 300 trillion cells]]
[[Image:cells_in_rest_en.png|thumb|left|In rest the heart cells are negatively charged. Through the depolarization by surrounding cells they become positively charged and they contract.]]
[[Image:Ion_currents_en.png|thumb|left|During the depolarization sodium-ions stream inwards the cell. Subsequently the calcium-ions stream into the cell. These calcium-ions give the actual muscular contraction. Finally the potassium-ions stream out of the cell. During the repolarisation the ion concentration is corrected. On the ECG, an action potential wave coming towards the electrode is shown as a positive (upwards) signal. Here the ECG electrode is represented as an eye.]]
The individual [[action potential|action potentials]] of the individual cardiomyocytes are averaged. The final result which is shown on the ECG is actually the average of trillions of microscopic electronical signals.


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