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.
An ST-elevation myocardial infarction (STEMI) is a combination of symptoms of chest pain and a specific STEMI EKG heart tracing. The EKG has to meet what is called STEMI criteria to make a correct diagnosis, just like an NSTEMI will provide another set of specific diagnostic criteria.