1. The Heart Continued... Human heartbeats originate from the SA node near the right atrium. Cardiac muscle cells contract, sending a signal to other muscle cells in the heart to contract.

2. The signal spreads to trigger the AV node Signals carried from the AV node, then spread and cause the ventricles to contract simultaneously.

3. Electrical Conduction

5. Measurement of Heart Contractions An electrocardiogram (ECG) measures changes in electrical potential across the heart –detects the contraction pulses that pass over the surface of the heart. –ECGs are useful in diagnosing heart abnormalities.

6. Electrical conduction across the heart The P wave represents the contraction impulse of the atria, the T wave the ventricular contraction.

7. Abnormalities