Various modalities. There are non-invasive tests to look for blockages such as stress echocardiography (stress test w/ultrasound imaging), nuclear myocardial perfusion imaging (nuclear medicine imaging), cardiac ct and MRI (mri is still investigational for coronary anatomy). Gold standard examination requires invasive cardiac catheterization with dye injected into the arteries (or ultrasound) and imaged.
Arteries. Atherosclerotic disease is ubiquitous, there is no such thing as single vessel disease. If you have it it, you have it and need systemic treatment to prevent progression. If you are concerned about having it, become a vegetarian, get at least half hour of aerobic exercise a day and get checked for risk factors to take care specifically.