Myocardial rupture (or heart rupture) is a laceration or tearing of the walls of the ventricles or atria of the...

Myocardial rupture (or heart rupture) is a laceration or tearing of the walls of the ventricles or atria of the heart, of the interatrial or interventricular septum, of the papillary muscles or chordae tendineae or of one of the valves of the heart. It is most commonly seen as a serious sequela of an acute myocardial infarction (heart attack).
It can also be caused by trauma.

For people who initially survive a heart attack, a significant cause of death in the next few days is cardiac rupture -- literally, bursting of the heart wall.
After a heart attack, the body produces a range of chemicals that trigger biological processes involved in healing and repair. Unfortunately, many of these chemical signals can become "too much of a good thing" and end up causing further damage often leading to heart failure and sudden death.

Know more about this: http://news-releases.uiowa.edu/2011/november/111711heart_rupture_study.html

Also, know more about diagnosis, treatment and prognosis of 
 cardiac rupture in acute myocardial infarction:
http://www.fac.org.ar/scvc/llave/coronary/figueras/figuerai.htm

Images via forensicpathologist