Blood leaks back into the chambers rather than flowing forward through the heart or into an artery. In the United States, backflow most often is due to prolapse. Prolapse is when the flaps of the valve flop or bulge back into an upper heart chamber during a heartbeat. Prolapse mainly affects the mitral valve.
NSTEMI is a shorthand medical term for non-ST segment elevation myocardial infarction. It is one type of myocardial infarction also called heart attack.
If the blockage is complete, a STEMI occurs. In a STEMI, the ST segments on the electrocardiogram become elevated (hence, the name), and cardiac enzymes greatly increase. These findings indicate that significant heart cell death is occurring. With unstable angina and NSTEMI, the blockage is not (yet) complete. Clinically, NSTEMI is identical to unstable angina except for one thing. In NSTEMI, in contrast to unstable angina, the cardiac enzyme blood tests are abnormal, indicating that at least some actual cell damage is occurring to heart muscle cells.