It is used to evaluate heart wall thickness and motion, the structure and function of the heart valves, and to estimate the amount of blood pumped out of your left ventricle with each heartbeat, (ejection fraction).
Specifically, an echo can:
identify areas of poor blood flow in the heart
identify areas of the heart muscle that are not contracting normally
identify areas of previous injury to the heart muscle
detect evidence of heart failure
detect a blood clot in the heart
evaluate the heart valves
detect pericardial effusion (fluid around the heart)