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ECG Experiments

Updated on January 30, 2013

This is a lab report I did during the class, which is Biology 242 at GRCC.


The Electrocardiogram (EKG/ECG) is a graphic tracing of the heart's electrical activity. There are five major deflections on a normal ECG and they represent one heart cycle. The P wave indicates the depolarization of the atria. The QRS wave complex represent depolarization of the ventricles. The T wave denotes repolarization of the ventricles.

Connecting the ECG Sensor to a Person and Collecting Data


1. Resting ECG

Record the ECG of a person who is at rest. The person whose ECG is being recorded should remain calm and relaxed.

Duration of Cardiac Cycle:0.9sec.

Heart rate: 67

2. ECG after mild exercise

After recording an ECG of a person who is at rest, have the person exercise for 3-5 minutes by stair stepping.

Duration of Cardiac Cycle: 0.57sec.

Heart rate: 105.3

What are the differences between the resting ECG and the ECG after exercise?

Duration of cardiac cycle is shorter and heart rate after exercise gets faster.

What caused the ECG after exercise to differ from that at rest?

Increase heart rate to supply more oxygenerated blood to body for exercise.

3. ECG and breathholding

Have the person take a deep breath, and while holding their breath, bear down for 5 sec.

Duration of Cardiac Cycle: 0.83sec.

Heart Rate: 72.29

What are the differences between the resting ECG and the ECG during breath holding?

There is no big differences but the duration of cardiac cycle of breathholding supposed to be slower than the duration of cardiac cycle of the resting.

What caused the ECG during breath holding to differ from that at rest?

ECG Review Questions

1. The electrocardiogram is a powerful tool used to diagnose certain types of heart disease. Why is it important to look at time intervals of the different waveforms?

By measuring time intervals on the ECG, how long the electrical wave takes to pass through the heart can be determined. Finding out how long a wave takes to travel from one part of the heart to the next indicates if the electrical activity is normal or slow, fast or irregular. (A delay in conduction in any portion of heart)

2. What property of heart muscle must be latered in order for an ECG to detect a problem?

ECG is a record of electrical activity of heart and the depolarization of cardiac-muscle cells generates the contraction. The cells of the heart's conducting system will depolarize spontaneously. So conductivity of heart muscle must be affected in order for an ECG to detect a problem.

3. Why can't an ECG be used to diagnose all diseases or defects of the heart?

ECG can't be used to detect all problems of heart because there are many variables. ECG only can detect electrical activities of heart. Not all diseases of heart involve a change in electrical activity.

4. Would a person with complete heart block survive? Why or why not?

Complete heart block is also known as third degree AV blcok. It can be fatal and result in sudden cardiac arrest and death. When complete heart blcok occurs, the impulse generated in the SA node in the atrium does not travel to the ventricles. This cause the ventricles to create electrical signals for contraction but it is slow and isn't coordinated with the contraction of the atria.


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