Optimal visualization of moving structures such as the heart and coronary arteries using digital radiographic imaging systems is a difficult problem that can involve tradeoffs between temporal, spatial, and density resolution. The motion dependence of four angiographic measures of vessel dimensions is given and demonstrated experimentally. Although the densitometric cross‐sectional area is shown to be independent of motion, densitometric thickness (contrast) decreases and the apparent width (distance between edges) and densitometric width both increase with motion. Knowledge of the velocity allows the apparent width but not the densitometric width to be corrected. It is also shown that current limitations which result in tradeoffs between kVp and x‐ray pulse duration seriously compromise the advantages of using small focal spots in coronary artery imaging.