A decrease in the cardiac function and intracellular calcium, and an increase in the cardiac sarcolemmal ATPase have been reported in aortic stenosis of 6 to 9 months duration in dogs. The present investigation deals with the effect of 3 months of digoxin treatment on cardiac function, electrolytes and ATPase in dogs with 3 months of aortic stenosis in order to determine whether digoxin treatment gives only haemodynamic improvement or if it also improves the condition of the myocardium in terms of contractility and biochemical changes. There were no significant changes in any of the haemodynamic parameters of left and right ventricles except the left ventricular end-diastolic pressure which increased significantly at 3 months of aortic stenosis. All the hearts developed left ventricular hypertrophy. Concomitant with these changes, there was a tendency for a decrease in the total tissue Ca2+, intracellular Ca2+ and K+, and a tendency for an increase in the sarcolemmal ATPase. There were no significant differences in any of the haemodynamic parameters between the aortic stenotic and digoxin treated aortic stenotic dogs indicating that digoxin was at least maintaining the haemodynamics close to the pretreatment level. Although digoxin treatment prevented the changes in the sarcolemmal ATPase and extracellular space, it did not prevent the further decrease in the total or intracellular Ca2+. The total and intracellular Ca2+ was still significantly higher than previously observed after 6 to 9 months of aortic stenosis. These results suggest that digoxin treatment not only tended to prevent further deterioration of cardiac function but also tended to prevent further changes in the sarcolemmal ATPase and electrolytes.