To determine whether anemia-induced cardiac hypertrophy affects ventricular size and shape and the component structures of the capillary network of the left and right ventricles, young male rats were fed an iron- and copper-deficient diet for 7 weeks. By that time, blood hemoglobin content fell to 5 +/- 1 g/dl, and packed cell volume fell to 18 +/- 3%. To further characterize the implications of anemia, red blood cell number, hemoglobin corpuscular content, systemic arterial pressure, heart rate, and blood viscosity were measured. Moreover, the changes in ventricular weights were analyzed in terms of the alterations in ventricular wall area and ventricular wall thickness to establish the impact of the elevation in load associated with a high cardiac output state on ventricular remodeling. The quantitative properties of the capillary circulation were also examined biventricularly by low power electron microscopic morphometry to evaluate the adaptive growth potential of the coronary microcirculation in this form of cardiac hypertrophy. Anemia was found to interfere with the production of red blood cells and their mean corpuscular hemoglobin content and resulted in a 40% reduction in blood viscosity and a 12% and 27% decrease in systolic and diastolic blood pressure, respectively. The changes in heart rate were not statistically significant. In comparison with control animals, heart weight increased by 50%, but the enlargement in right ventricular mass (65%) was greater than that of the left ventricle (47%). Ventricular hypertrophy occurred with increases in wall area and wall thickness although the former increased consistently more than the latter in either ventricle. Tissue growth was accompanied by a 60% lengthening of the capillary network, which in combination with an increase in capillary diameter resulted in a 65% and 34% expansion in capillary luminal volume and 56% and 20% larger luminal surface density in the left and right sides of the heart, respectively. In conclusion, hypochromic microcytic anemia leads to eccentric ventricular hypertrophy with a significant amount of capillary proliferation that may tend to protect the myocardium from the increased potential for ischemic injury.