**Core Concept**
Doxorubicin, a chemotherapeutic agent, can cause cardiotoxicity leading to heart failure, particularly when used in high doses or for prolonged periods. This is due to its ability to intercalate DNA strands and generate free radicals, leading to mitochondrial damage and impaired energy production in cardiac myocytes.

**Why the Correct Answer is Right**
The symptoms described in Sunder, such as breathlessness on exertion (dyspnea) and nocturnal dyspnea, are classic manifestations of heart failure. The swelling in his feet (edema) is also a common finding in heart failure, indicating fluid overload. Doxorubicin-induced cardiotoxicity can lead to left ventricular dysfunction, resulting in these symptoms. The mechanism involves the generation of reactive oxygen species (ROS) that damage cardiac myocytes, leading to impaired contractility and eventually heart failure.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the clinical scenario described. While anemia can cause fatigue and shortness of breath, it does not explain the nocturnal dyspnea or edema.

**Option B:** While pulmonary embolism can cause sudden onset of dyspnea, it does not typically present with nocturnal dyspnea or edema. Additionally, there is no mention of any risk factors for pulmonary embolism in the scenario.

**Option C:** This option is not directly related to the symptoms described. While Sunder's leukemia treatment may have caused fatigue, it does not explain the specific symptoms of heart failure.

**Clinical Pearl / High-Yield Fact**
Doxorubicin-induced cardiotoxicity is a well-known side effect of this chemotherapeutic agent, particularly with high cumulative doses. It is essential to monitor cardiac function regularly in patients receiving doxorubicin-based regimens.

**Correct Answer:** C. Tricuspid regurgitation is not directly mentioned in the options, however, the correct answer is likely related to **C. Cardiac issues**.