What defines the primary effect of digoxin in heart failure treatment?

The primary effect of digoxin in the treatment of heart failure is improved contractility. Digoxin enhances the force of contraction of the heart muscle by inhibiting the sodium-potassium ATPase pump, which leads to an increase in intracellular sodium and subsequently increases calcium levels in the cardiac cells. This increase in calcium strengthens the myocardial contraction, improving cardiac output and helping to alleviate symptoms associated with heart failure.

While addressing other choices, it is important to note that digoxin does not primarily increase heart rate; in fact, it often has a slowing effect on the heart rate by enhancing vagal tone. Additionally, digoxin does not decrease preload significantly; preload is mainly influenced by fluid status and venous return, rather than direct effects of digoxin. Furthermore, digoxin is not known to cause increased sodium retention; rather, it can have a role in the management of fluid status, but this is not its defining action in the context of heart failure treatment.