In the catheter laboratory, faced with a patient with unstable angina, the problem is not the diagnosis of epicardial coronary artery stenosis but rather the atherothrombotic complexity of the stenosis and the identification of other less stenotic lesions on angiographically normal or nearly normal segments. The authors describe two appearances with morphological analysis of the vulnerable or unstable plaque and functional analysis of coronary artery vasomotricity. Acute coronary syndromes due to a clearly stenotic atherothrombotic plaque on angiography pose no diagnostic problems. However, an acute coronary syndrome may be more difficult to assess when angiography shows only simple irregularities of the lumen or no lesions at all. In these cases, angiography is said to be normal and the coronary arteries are considered to be possibly "healthy". Evaluation of the vessels' vasomotricity is especially valuable in this context. Using pharmacological stress tests, endovascular ultrasonography is a complementary diagnostic tool which allows identification of the unstable atheromatous process or of a partial atherothrombosis masked by positive remodelling process. These tests may also indicate the optimal treatment.