A new technique was developed for analyzing the neovascularization associated with coronary artery atherosclerosis: cinematography during silicone polymer injection of the coronary arteries of fixed and cleared human hearts, followed by histologic analysis in routine and 1-micron-thick, Epon-embedded sections. Twenty-two hearts obtained at autopsy were studied. On the basis of cinematographic findings, individual regions of the coronary arteries were classified as negative, positive, or abundantly positive for neovascularization. Positive and abundantly positive areas, which invariably occurred in segments exhibiting changes of atherosclerosis, contained numerous small vessels in the adventitia and outer media (4.7 +/- 1.5 and 9.8 +/- 1.3 [SE] vessel profiles/artery cross-section in positive and abundantly positive areas, versus 1.0 +/- 0.6 in negative regions). Abundantly positive areas, which occurred in coronary artery segments demonstrating the most extensive atherosclerotic change, contained numerous small vessels in the inner media or in the plaque itself. Some of these microvessels were in close proximity to mast cells, which represent potentially rich sources of mediators affecting vascular tone and permeability. Vessels were not observed in the inner media or in atherosclerotic plaque in areas designated either positive or negative by cinematography. These findings show how our approach can be used both to define the three-dimensional, in situ configuration of coronary artery neovascularization and to characterize the histology of this process in detail. They also confirm previous work indicating that areas of coronary arteries involved by atherosclerosis frequently exhibit extensive neovascularization.