Echocardiography or echo is a painless test that uses sound waves to create moving pictures of your heart. This test allows your doctor to monitor the shape and size of the heart and how well the chambers and valves are functioning. Echo can pinpoint areas of the heart muscle that aren't contracting well because of poor blood flow or injury from a previous heart attack. It can detect blood clots inside the heart and fluid buildup in the sac around the heart.