Magnetic resonance imaging (MRI) is a powerful tool which enables the visualization of anatomy and the assessment of many physiological aspects of organ function. MRI and magnetic resonance angiography and magnetic resonance spectroscopy will play critical roles in cardiac applications during the next millennium. Thus, it is important to have a basic understanding of the most important physical processes in MR--the generation of nuclear magnetic resonance signals and their transformation into images. A conceptual description of these processes is the primary focus of this article. Also discussed are some additional signal manipulations specific to the needs of cardiac MRI, a field readily identified as the most significant in modern MRI technology development.