These tests are valuable diagnostic tools in the detection of cardiac disease and its problems. Cardiac stress testing is a must in identifying partial blockages in the coronary arteries. Coronary artery disease will be missed when at rest, but becomes evident only when performing certain exercises. After obtaining a base line ECG, perform a low level exercise by means of walking on a thread mill or pedaling a stationary bi cycle. According to the exercise, it is graded every 3 minutes and at each stages your pulse, BP, ECG will be recorded. In case of maximal stress test, the exercise is increased until you become fatigue; complain of chest pain, shortness of breath or light-headedness. Whereas in case of Sub Maximal stress test only up to a specific level is done because you are already having CAD. It can also detect evidence of myocardial infarction and also cardiac arrhythmias due to increased adrenaline levels. With relevance to your question, you should read number of books on stress testing written on the subject by Dr Edward K Chung which might clear your doubts.