**Core Concept**
The cardiotoxicity of local anesthetics is primarily due to their effect on the cardiac ion channels, particularly the sodium channels, leading to a disturbance in the normal electrical activity of the heart. This can result in arrhythmias, cardiac arrest, and even death.

**Why the Correct Answer is Right**
The cardiotoxicity of local anesthetics is directly related to their ability to block sodium channels in the heart. Among the commonly used local anesthetics, Bupivacaine is known to have a high affinity for cardiac sodium channels, making it more cardiotoxic than other local anesthetics. This is because Bupivacaine can cause a significant depression of cardiac contractility and conduction, leading to severe arrhythmias and cardiac arrest. The mechanism of Bupivacaine-induced cardiotoxicity is thought to involve the blockade of sodium channels, leading to a prolonged depolarization of cardiac cells and a subsequent decrease in cardiac contractility.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while Lidocaine is also a local anesthetic, its cardiotoxic effects are generally considered to be lower than those of Bupivacaine. Lidocaine is actually used to treat certain types of arrhythmias due to its ability to block sodium channels in the heart.
**Option B:** This option is incorrect because Ropivacaine is a local anesthetic that is considered to be less cardiotoxic than Bupivacaine. Ropivacaine has a lower affinity for cardiac sodium channels, making it a safer choice for patients with cardiac disease.
**Option D:** This option is incorrect because Mepivacaine is a local anesthetic that is generally considered to be less cardiotoxic than Bupivacaine. Mepivacaine has a lower affinity for cardiac sodium channels, making it a safer choice for patients with cardiac disease.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the cardiotoxicity of local anesthetics is highly dependent on the dose and concentration used. Bupivacaine is a potent local anesthetic that should be used with caution in patients with cardiac disease. A memorable way to recall the cardiotoxicity of local anesthetics is to remember that Bupivacaine is the "B" in the acronym "BADD" which stands for "Bupivacaine-induced Arrhythmias, Depression, and Death".

**Correct Answer:** C. Bupivacaine.