Typical recording

A typical recording is shown below. The first, smaller contraction is that of the atria and the second larger contraction is that of the ventricle. Sometimes the smaller contraction of the sinus venosus can be seen slightly preceding the atrial contraction. From the recorded trace it is possible to determine the heart rate (beats/min) and the amplitude of both ventricular and atrial contraction (g). Remember the heart pacemaker, located in the sinus venosus, determines heart rate. The force of ventricular contraction determines the stroke volume of the heart.

In this example:

1. the heart rate is approximately 50 beats / minute
2. the amplitude of the ventricular contraction is 6g
3. the amplitude of the atrial contraction is 3g