An echocardiogram uses an ultrasound to evaluate the function of the heart muscle and valves. In a cardiac echo test, a technician creates moving images of the heart by pressing a wand-like ultrasound device against the chest. For a cardiac MRI, on the other hand, the patient lies on a bed scanner. The combination of magnetic fields and radio waves produces 3D images that are significantly crisper and more detailed than a traditional 2D echocardiogram.