**Core Concept**
Local anaesthetics are a class of medications used to prevent pain by blocking the conduction of nerve impulses. However, they can also have cardiotoxic effects, particularly when administered in high doses or through certain routes. The cardiotoxicity of local anaesthetics is primarily related to their ability to block sodium channels in the heart, leading to abnormal heart rhythms and potentially life-threatening complications.

**Why the Correct Answer is Right**
The cardiotoxicity of local anaesthetics is highly dependent on their lipid solubility and the rate at which they are metabolized by the liver. Bupivacaine is a highly lipid-soluble local anaesthetic that is metabolized slowly, making it more prone to cardiotoxicity than other agents. When bupivacaine is administered in high doses or through certain routes, such as intravenous or epidural, it can accumulate in the heart and block sodium channels, leading to abnormal heart rhythms, including ventricular fibrillation. The cardiotoxic effects of bupivacaine can be particularly severe and are often irreversible.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while lidocaine is also a local anaesthetic, it is less cardiotoxic than bupivacaine due to its lower lipid solubility and faster metabolism.
**Option B:** This option is incorrect because ropivacaine, a newer local anaesthetic, has a lower cardiotoxic profile than bupivacaine due to its lower lipid solubility and more rapid metabolism.
**Option D:** This option is incorrect because mepivacaine, another local anaesthetic, is less cardiotoxic than bupivacaine due to its lower lipid solubility and faster metabolism.

**Clinical Pearl / High-Yield Fact**
Bupivacaine-induced cardiotoxicity is often irreversible and can be fatal. Emergency treatment typically involves administering intravenous lipid emulsions to bind and remove the bupivacaine, as well as performing cardioversion or defibrillation to restore a normal heart rhythm.

**Correct Answer: C. Bupivacaine**