**Core Concept**
Peripartum cardiomyopathy (PPCM) is a rare condition characterized by the onset of heart failure in the last month of pregnancy or within 5 months after delivery, in the absence of any other identifiable cause of cardiomyopathy.

**Why the Correct Answer is Right**
The pathophysiology of PPCM is not fully understood but is thought to involve a combination of factors, including increased blood volume, cardiac hypertrophy, and potential autoimmune mechanisms. The condition is often associated with a decline in left ventricular ejection fraction (LVEF) and an increase in left ventricular end-diastolic diameter (LVEDD). The diagnosis of PPCM requires the exclusion of other causes of cardiomyopathy, such as hypertension, coronary artery disease, and cardiotoxic effects of medications.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the definition of PPCM specifically excludes heart failure that occurs earlier in pregnancy. PPCM typically presents in the last month of pregnancy or within 5 months postpartum.
**Option B:** This option is incorrect because PPCM is a specific diagnosis that requires the exclusion of other causes of cardiomyopathy. A diagnosis of PPCM cannot be made based solely on the presence of heart failure in the postpartum period.
**Option C:** This option is incorrect because PPCM is typically defined as the occurrence of cardiac failure within 5 months of delivery, not 6 months.

**Clinical Pearl / High-Yield Fact**
PPCM is a leading cause of maternal mortality in developed countries, and prompt recognition and treatment are essential to improve outcomes. A high index of suspicion is necessary for the diagnosis of PPCM, particularly in patients with risk factors such as advanced maternal age and history of hypertension.

**Correct Answer:** C.