Final answer:
When HR is below 60 despite effective ventilation, you follow the protocol leading to Block C, which involves further emergency interventions like medication or pacing to stabilize the patient.
Step-by-step explanation:
If the heart rate (HR) is below 60 even after effective ventilation, you proceed to Block C. This is likely referring to a protocol followed in emergency medicine or advanced cardiovascular life support (ACLS) when a patient is experiencing bradycardia (low HR) with poor perfusion, despite adequate oxygenation from effective ventilation. Block C refers to the next step or intervention in a structured protocol designed to support and stabilize the patient. This may involve additional interventions such as administrating medication, pacing, or other advanced life-saving measures.