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D. The Two Phases Of A Heart Attack

Narrator: This is Science Today. There are two phases of injury in a heart attack. First, a blood clot forms in a coronary artery and deprives blood flow. Then there's a second phase which Marcus Horwitz, a professor of medicine and infectious diseases at UCLA, says occurs after the initial blood clot.

Horwitz: When a patient comes to the hospital and that clot is opened up, either because a clot busting drug is given or a catheter is put in to open it up, then blood flows into the heart and that's good because it salvages heart tissue. But what's bad is, that there's a second phase of injury and this is less well appreciated but it's called reperfusion injury.

Narrator: During this phase, white blood cells release toxic oxygen molecules which can ultimately lead to congestive heart failure.

Horwitz: People survive their heart attacks more frequently today because of all the interventions of the recent decades. But a lot of the people who survive have damaged hearts and because of that, they have congestive heart failure which severely limits their activities.

Narrator: For Science Today, I'm Larissa Branin.