Refractory Period

Cardiac muscle fibres have a long refractory period and remain inexcitable for some time after the generation of an action potential. The duration of this refractory period can be determined by applying an electrical stimulus to the ventricle at different stages during the cardiac cycle. In this experiment, records are shown of the effect of applying an electrical stimulus:

1. during ventricular contraction
2. during ventricular relaxation

The point of stimulation is indicated on the trace by an arrow.

Task
You should observe the effect of stimulation on the heart beat and draw the response.

Use the play/pause button to halt the display to enable you to take your measurements more easily.