Explain the effect that extreme vagus nerve stimulation had on the heart. how well did the results compare with your prediction?

For the answer to the question above, I believe that the answer to your question is that the heart rate will decrease if there's an extreme vagus nerve stimulation The vagus nerve is part of the parasympathetic nervous system. The sympathetic nervous system is the "fight or flight" part of the autonomic nervous system, whereas the parasympathetic is the "feed or breed" part. The sympathetic side acts to speed things up; it increases heart rate, the blood pressure, also the respiratory rate, it dilates pupils, shunts blood away from the GI tract, and so on...
The parasympathetic the opposite in which acts to slow things down; it lowers down the heart rate or decrease blood pressure, it increases salivation, increase blood flow to the GI tract, and so on. The two systems are always balancing each other. The confusing part is that when you INCREASE the activity of the parasympathetic nervous system you DECREASE the activity of the heart; so increased vagal tone will slow the heart rate, decreases the contractility, and lowers blood pressure. When the heart is excitable and has certain types of arrhythmia, increasing the vagal stimulation can slow the heart down enough to allow the normal pacemaker functions to take over again also called as converting.

Examples of vagus nerve stimulation is the Valsalva maneuver as well as massaging the carotid area. The extreme vagus nerve stimulation will produce a significant decrease in heart rate because the vagus nerve has autonomic functions, specifically primarily parasympathetic output. Parasympathetic stimulation of the heart decreases the conduction velocity (negative dromotropic effect) of the impulses from the sinuatrial node to the Purkenji fibers therefore decreasing the overall heart rate (negative chronotropic effect).