How accurate is an ultrasound in detecting heart failure, heart disease and clogged arteries? is a good result that is about 18 months old reliable?

It depends: An ultrasound can measure how well the heart beats by measuring the activity of the heart muscle. So it can accurately measure heart failure. However, it cannot measure other abnormalities such an accute heart attack or clogged arteries or conduction problems. An angiogram is the gold standard for detecting clogged arteries. Other tests such as ECG or blood tests are used to diagnose an accute mi.

Pretty accurate : You can never see clogged arteries on ultrasound, but can be indirectly assessed by wall motion. An 18 month old result is not reliable.