Coronary artery disease (CAD) can cause poor blood flow and supply to the heart muscle. It can result in irreversible damage to the heart muscle and poor function. Before treating patients with heart disease it is important to know how well the heart is functioning. Echocardiography is a diagnostic test that can measure heart function. If part of the heart muscle is not working properly due to previous damage, echocardiography can provide information about how much improvement can be expected after treatment (surgery or angioplasty).