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.
NSTEMI refers to non-ST elevation myocardial infarction. That is, parts of the heart muscle is infarcting without any ST elevations on the 12 lead EKG. Usually evidence of a NSTEMI is determined based on serial troponins (a cardiac enzyme). If there is any measurable amount of troponin in the blood, then heart muscle damage, of some sort, has occurred. In the absence of some other cause (PE, for instance, can cause a troponin elevation), NSTEMI is diagnosed.