I think your teachers are wanting you to look at the effect of myocardial damage on the pumping ability of the heart and the sequelae of events that would follow decreased pumping ability. MI ==>damaged heart muscle ==>lowered ejection fraction ==>decreased blood pumping out==>kidneys can "sense" the reduction in flow and all of the compensatory mechanisms are initiated. The renin-angiotensin-aldosterone system comes into play==>body conserves fluid in an attempt to increase the total volume.
These compensatory mechanisms work fine in the short run, but after awhile this increase in total volume puts an even greater workload on the heart and leads to congestive heart failure. You should focus your research on the electrolytes involved in these processes (Na, K. etc.)
Also, realize that an acute loss of blood supply to the cardiac muscle causes rapid depletion of potassium from the ischemic musculature (from Guyton textbook of Phys.), this increases potassium in the extracellular fluids surrounding the cardiac muscle fibers and in turn increases the irritability of the heart.