Final answer:
A third-degree block is a cardiac conduction disorder where there is no correlation between atrial and ventricular activity. This can lead to a slower heart rate.
Step-by-step explanation:
A third-degree block is a type of cardiac conduction disorder where there is no correlation between atrial activity (the P wave) and ventricular activity (the QRS complex). In this condition, some of the impulses initiated by the SA node do not reach the AV node, while others do. As a result, the heart rate (pulse) is usually slower, ranging from 40 to 60 beats per minute (bpm).