What is the primary action of hydralazine in managing heart failure?

Hydralazine primarily acts as a vasodilator, which leads to a decrease in afterload in patients with heart failure. By relaxing the smooth muscle within the arterial walls, hydralazine reduces systemic vascular resistance. This reduction in afterload decreases the workload on the heart, allowing it to pump more effectively and improving cardiac output.

In the context of heart failure, managing high afterload is crucial, as a high resistance can hinder the heart's ability to eject blood efficiently. Lowering afterload helps to improve symptoms and may enhance exercise tolerance for patients with heart failure.

The other actions mentioned, such as decreasing preload or increasing contractility, do not directly describe the principal effect of hydralazine. While controlling arrhythmias is another important aspect of heart failure management, hydralazine is not primarily used for that purpose; its main role is in reducing the stress placed on the heart by lowering afterload.