## **Core Concept**
Cardiac glycosides are a class of medications used to treat heart conditions, such as atrial fibrillation and heart failure. They are derived from specific plant sources and work by inhibiting the **Na+/K+-ATPase pump**, leading to increased cardiac contractility and reduced heart rate. The primary plant sources of cardiac glycosides include *Digitalis purpurea*, *Digitalis lanata*, *Strophanthus gratus*, and *Convallaria majalis*.

## **Why the Correct Answer is Right**
The correct answer, *, is right because it corresponds to* Digitalis purpurea, *commonly known as foxglove, which is a well-known source of cardiac glycosides, specifically **digoxin**. Digoxin is used clinically to increase the force of cardiac contractions and slow the heart rate in conditions like atrial fibrillation and congestive heart failure.

## **Why Each Wrong Option is Incorrect**
* **Option A:** * is incorrect because, although* Strophanthus gratus *is a source of cardiac glycosides (e.g., ouabain), it does not match the correct answer.*
* **Option B:** * is incorrect as it does not directly correspond to a commonly recognized plant source of cardiac glycosides in a straightforward manner.*
* **Option C:** * is incorrect because while there are multiple plant sources of cardiac glycosides, the correct and specific match for* . *is not provided here but* Convallaria majalis *(lily of the valley) is another plant source.*

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that cardiac glycosides, such as **digoxin**, have a narrow therapeutic index, meaning the difference between an effective dose and a toxic dose is small. Monitoring of serum levels and renal function is crucial when using these medications.

## **Correct Answer:** .