Which medication is known as a cardiac stimulant?

Digitalis is recognized as a cardiac stimulant primarily due to its active compounds, such as digoxin, which enhance the force of the heart's contractions. This property is particularly beneficial in managing certain heart conditions, including atrial fibrillation and heart failure. By increasing the strength of heart muscle contractions, digitalis can help improve blood flow and alleviate symptoms associated with these cardiac conditions.

In the context of this question, aspirin is primarily an antiplatelet medication used to reduce blood clot formation; furosemide is a diuretic used to manage fluid retention; and phenobarbital is a barbiturate used mainly for seizure control and sedation, none of which exhibit properties that stimulate the heart in the way digitalis does. Thus, digitalis stands out as the only medication in this list that functions specifically as a cardiac stimulant.