The pathomechanisms responsible for the development and progression of myocardial alterations in hypertensive heart disease are largely unknown. Using newly developed preparation and measuring procedures in 78 SHR and 82 controls aged 3-78 weeks, topological relations were detected between focal morphological appearances of chronic myocardial ischemia (fml.) and pathological microvessel (mv.) reactions characterized by morphometric signs of chronic contractions. The smallest ramifications are of particular pathogenic importance. A generalized peak of pathological mv. reactions between the 16th and 24th weeks is responsible for the development of first fml. The further progression of the area density of fml. from 1.26 +/- 0.85% (24th week) to 31.82 +/- 8.60% (78th week) is attributable to the further increase in pathological mv. reactions caused by organ-specific influences. The histological and morphometric findings suggest that the pathological mv. reactions are aggravated by their own effects at the local level.