**Core Concept**
The question is testing knowledge on the leading cause of maternal mortality, which is a critical aspect of obstetrics and gynecology. Maternal mortality refers to the death of a woman due to complications related to pregnancy or childbirth.

**Why the Correct Answer is Right**
The World Health Organization (WHO) identifies hemorrhage as the leading cause of maternal mortality worldwide, accounting for approximately 27% of all maternal deaths. This is due to the sudden and severe loss of blood, which can lead to shock, organ failure, and death. Hemorrhage can occur due to placental abruption, uterine rupture, or postpartum hemorrhage.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypertension is a significant risk factor for maternal mortality, but it is not the leading cause. Hypertension can lead to complications such as eclampsia, placental abruption, or stroke, but it is not the primary cause of maternal death.
**Option B:** Sepsis is a major cause of maternal morbidity, but it is not the leading cause of maternal mortality. Sepsis can occur due to infections such as puerperal sepsis or urinary tract infections, but it is not as common as hemorrhage as a cause of death.
**Option C:** Cardiac diseases are a significant cause of maternal mortality, especially in developed countries. However, they are not the leading cause globally, and hemorrhage remains the number one cause of maternal death.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize the signs of hemorrhage, including vaginal bleeding, shock, and tachycardia, and to provide immediate medical attention to prevent maternal mortality.

**Correct Answer: C. Hemorrhage**