In 100 consecutive deaths from a coronary care unit, the coronary arteries were examined microscopically in longitudinal sections (serial and semi-serial) so that the entire extramural part of each artery was scrutinized. Occluded coronary arteries were found in 88 cases, the occlusions being due to thrombi in 17, to the contents of soft atheromatous plaques in 22, and to a mixture of soft plaque content and thrombus in 49; thus in 71 cases the coronary occlusions are due basically to the rupture of soft plaques. After deep-freezing, the entire myocardium of each heart was examined naked eye in serial slices (using Nitro-BT) and selected areas microscopically. The findings allowed tentative groupings into single episode, double episode, and progressive lesions according to age structure. Correlation of the coronary and myocardial findings has been attempted.