Final answer:
A child with low blood pressure and wheezing likely ingested a beta blocker, which can cause these symptoms due to its action of blocking adrenaline and reducing heart rate.
Step-by-step explanation:
The child who was rushed to the hospital after taking his grandmother's blood pressure medication has symptoms of low blood pressure and trouble breathing with wheezing upon exhalation. These symptoms strongly suggest that the child most likely ingested a beta blocker. Beta blockers are common medications prescribed for high blood pressure and they work by blocking G-protein-linked receptors in the heart muscles, which in turn blocks adrenaline. This leads to a decreased heart rate (HR) and can be an effective treatment for hypertension, but an overdose can cause bradycardia, difficulty breathing, and potentially even heart stoppage.