Primacor, known generically as milrinone, is a type of medication classified as a phosphodiesterase 3 inhibitor. It is primarily used in the treatment of acute decompensated heart failure, where it works by helping to relax and widen blood vessels and decrease the strain on the heart, making it easier for the heart to pump blood. Primacor is administered intravenously under close medical supervision, typically in a hospital setting. Its action helps to improve symptoms such as shortness of breath and swelling in people with heart failure. As with any medication, it is essential to use Primacor under the guidance of a healthcare professional, as it can have significant side effects and interactions with other medications.