heparin

Heparin is the fast-acting, injectable anticoagulant of acute cardiac care — the one reached for when clotting must be slowed within minutes, not days. Where warfarin works slowly through the liver, heparin works directly in the bloodstream, so it is the tool for emergencies and procedures.

It works by supercharging a natural brake on clotting called antithrombin, helping it shut down thrombin and factor Xa far faster than it would alone. It comes in two main forms: unfractionated heparin, given by vein and adjusted with blood tests, and low-molecular-weight heparin, given as predictable under-the-skin injections.

In cardiology it is used during heart attacks, in unstable angina, around stent procedures, and to treat or prevent venous clots, especially in hospitalized patients. Its rapid on-off action and, for unfractionated heparin, a reliable reversal agent make it well suited to the unpredictable rhythm of acute care.

Beyond bleeding, heparin carries a specific caveat: a small number of people develop heparin-induced thrombocytopenia, an immune reaction that paradoxically lowers platelets and can trigger clots, so platelet counts are watched during longer courses.