This is a fatal myocardial infarct (heart attack). A portion of the heart has died as a result of occlusion of its blood supply. The mechanism of death in this case was physical rupture of the heart muscle through the weakened dead area.
The first picture shows the rupture point, as a deep mark surrounded by brighter red where the blood spread out through the epidardial fat.
The second picture shows coagulation necrosis of the myocardial fibers, and the neutrophils which have come in to be sure the area is not infected with bacteria. Both the cell death itself and the neutrophil enzymes weaken the tissue.
Not all heart attacks can be prevented, but today with lifestyle changes and/or medication, most people can cut their risk substantially.