A postmortem study of the capacity of the coronary arteries is presented. The amount of injected Schlessinger's barium-gelatin mass taken up by the coronary arterial tree under standard conditions was used as a measure of coronary capacity. A total of 63 hearts, consisting of those with Chagas' cardiopathy, normal hearts, and hypertrophied hearts, were studied. Correlation coefficients between coronary capacity and heart weight, as well as index of coronary capacity based on heart weight, were the parameters submitted to statistical analysis. Positive correlation coefficients between coronary capacity and heart weight were detected in normal and chagasic cases but not in hypertrophied cases. Multiple comparisons of the indexes showed a highly significant increase of coronary capacity in chagasic cases when compared with normal (p less than 0.005) and hypertrophied hearts (p less than 0.01). The characteristic parasympathetic denervation, resulting in a relative sympathetic overdrive, is suggested to be the basic cause of enlargement of the coronary tree in Chagas' heart disease, thus providing further support for the neurogenic pathogenetic concept.