True or False: A premature junctional contraction occurs when an irritable site within the AV junction fires prematurely?

A premature junctional contraction (PJC) does indeed occur when an irritable site within the atrioventricular (AV) junction fires prematurely. This can happen when the AV node or surrounding tissue becomes excitable, leading to a beat that interrupts the normal sinus rhythm. In essence, the heart has a built-in protective mechanism, and when the regular pacemaker activity is disrupted by these irritations, the AV junction can take over to initiate a contraction.

This phenomenon is characterized by an early heartbeat that originates from the junctional area, which is located between the atria and ventricles of the heart. This is consistent with the definition of a PJC, making the statement true. The key aspect is the "premature" nature of the contraction, emphasizing that it occurs outside the normal timing of the heart's rhythmic activity. Therefore, recognizing that PJCs arise from this specific area and under these conditions confirms the accuracy of the statement.