**Question:** Infantile myocarditis and pericarditis is due to –

**Core Concept:** Infantile myocarditis and pericarditis are inflammatory conditions affecting the heart muscle (myocardium) and the outer lining of the heart (pericardium) in infants, respectively. They can be caused by various factors.

**Why the Correct Answer is Right:** Infantile myocarditis and pericarditis are generally caused by viral infections, particularly enteroviruses like Coxsackievirus and echoviruses. These viruses can invade the heart tissue, leading to inflammation and damage.

**Why Each Wrong Option is Incorrect:**

A. **Myocarditis due to bacteria (e.g., Streptococcus pyogenes)**: This is incorrect because the question specifically mentions "infantile" myocarditis, implying viral etiology. Bacterial infections typically cause adult-onset myocarditis and are not specific to infants.

B. **Pericarditis due to bacteria (e.g., Streptococcus pyogenes)**: Similar to option A, this answer assumes adult-onset pericarditis, which is not the focus of the question. Infections by bacteria like Streptococcus pyogenes can cause pericarditis in infants, but viruses are more common in this age group.

C. **Neonatal viral infections**: Although neonatal infections can involve myocarditis and pericarditis, the question specifically mentions "infantile" forms, which are generally due to viral infections like those mentioned earlier.

D. **Neonatal bacterial infections**: Neonatal infections can cause myocarditis and pericarditis but, as mentioned before, infantile cases are more commonly viral in nature.

**Clinical Pearl / High-Yield Fact:** Infantile myocarditis and pericarditis are often associated with other clinical manifestations, such as fever, respiratory distress, and feeding difficulties. Early diagnosis and treatment are crucial to prevent complications like heart failure and arrhythmias. In severe cases, these conditions may lead to heart dysfunction and failure.

**Correct Answer:** C. Neonatal viral infections: Infantile myocarditis and pericarditis are commonly associated with viral infections, particularly enteroviruses like Coxsackievirus and echoviruses. These viruses can cause inflammation and damage to the heart tissue, leading to the clinical manifestations mentioned earlier.