Which drug is contraindicated in patients with heart block?

Beta blockers are contraindicated in patients with heart block because they can further depress cardiac conduction. In the case of heart block, there is a disruption in the electrical signals that coordinate heartbeats, leading to an ineffective heart rhythm. Beta blockers exert their effect by slowing the heart rate and reducing conduction through the atrioventricular (AV) node, which can exacerbate the existing conduction issue in patients with heart block. This increases the risk of more severe bradycardia or complete heart block, potentially worsening the patient's condition.

In contrast, calcium channel blockers may also affect heart rate and conduction but are generally used with caution rather than outright contraindicated in specific situations depending on the type of heart block. Angiotensin converting enzyme inhibitors and diuretics do not have direct implications on the heart's electrical conduction system and are typically not contraindicated in patients with heart block, as their primary functions are related to blood pressure management and fluid balance.