**Core Concept**
Maternal mortality refers to the number of deaths among women due to complications related to pregnancy or childbirth, per 100,000 live births. Direct causes of maternal mortality are those that occur during pregnancy, childbirth, or the postpartum period, and are directly related to the pregnancy itself.

**Why the Correct Answer is Right**
Heart disease is a leading cause of mortality in women, but it is not a direct cause of maternal mortality. Maternal mortality is defined as death occurring during pregnancy, childbirth, or the postpartum period, and heart disease is not directly related to these events. In contrast, antepartum hemorrhage (APH), postpartum hemorrhage (PPH), and eclampsia are all direct causes of maternal mortality because they can lead to severe complications and death during pregnancy or childbirth.

**Why Each Wrong Option is Incorrect**
**Option A:** Antepartum hemorrhage (APH) is a direct cause of maternal mortality because it can lead to severe bleeding and shock during pregnancy.
**Option B:** Postpartum hemorrhage (PPH) is a direct cause of maternal mortality because it can cause severe bleeding and shock after delivery.
**Option D:** Eclampsia is a direct cause of maternal mortality because it can cause seizures and coma during pregnancy or childbirth.

**Clinical Pearl / High-Yield Fact**
Remember that direct causes of maternal mortality include any condition that occurs during pregnancy, childbirth, or the postpartum period, and is directly related to the pregnancy itself. Indirect causes of maternal mortality, on the other hand, are conditions that occur during pregnancy or childbirth, but are not directly related to the pregnancy itself.

**Correct Answer:**
✓ Correct Answer: C. Heart disease.