In which part of the cardiac cycle can a strong ventricular stimulus become dangerous?

The correct choice emphasizes the T wave of the cardiac cycle. The T wave represents the repolarization of the ventricles, which is a critical moment in the cardiac cycle where the heart muscle is preparing for the next contraction. If a strong ventricular stimulus occurs during this phase, it can lead to dangerous arrhythmias, such as Torsades de Pointes or ventricular fibrillation. This is largely due to the heart muscle being in a vulnerable state as it recovers from depolarization.

During other parts of the cardiac cycle, such as the P wave or the QRS complex, strong stimuli are less likely to lead to dangerous outcomes. The P wave corresponds to atrial depolarization and does not directly reflect the ventricles' recovery state. The QRS complex indicates ventricular depolarization, at which time the cardiac muscle is actively contracting, and a strong stimulus here may not have the same disruptive effects as during the repolarization phase.

Focusing on the T wave highlights the sensitivity of the heart's electrical activity during repolarization and illustrates why a strong stimulus during this interval can have severe consequences on the overall rhythm of the heart.