As far as equipment is concerned, you would only need a watch. You can use your fingers to take a person's pulse rate. There are devices which will measure pulse rate, but they can be expensive and your fingers will suffice.
To calculate pulse rate, find the person's heartbeat on the inside of the wrist with your fingertips. Keeping your eye on your watch, count the beats for fifteen seconds, then multiply the number of beats by four. This will give you pulse rate in beats per minute (BPM).
Chose several durations of light exercise. For example, you could ask your subject to jog in place for 5, 10 or 15 minutes. Before he/she begins, find their BPM at rest. As soon as the subject finishes the exercise period, find their BPM again. Continue to do so at regular intervals (for example, every two minutes) until their heart rate returns to the resting rate.
To examine the quantitative effects, it might be interesting to plot your results on one graph. You should have BPM on the y-axis and time on the x-axis. Graph your results such that t=0 is equal to the end of the exercise period. You should have three curves on the graph.
Some interesting characteristics to compare between the three curves will be maximum BPM and time to return to normal BPM.