Systolic myocardial contraction may produce changes in coronary resistance and capacitance that persist throughout a normal diastole. In addition, coronary resistance and capacitance as determined in the arrested heart may not accurately describe normal diastolic behavior. To evaluate these possibilities, an identification method capable of characterizing the input impedance of the coronary circulation in as little as 150 ms was developed. Using this method, coronary dynamics were measured during early and late diastoles in the beating heart with tone intact as well as during adenosine-induced maximal vasodilation. Coronary dynamics were also measured in the arrested heart during maximal vasodilation. With vasomotor tone intact, the parameters of a lumped model of the coronary circulation showed no variation from early to late diastole. During maximal vasodilation, model parameters also showed no variation from early to late diastole. Parameters in the arrested heart were not statistically different from those of the beating heart during maximal vasodilation. However, model parameters determined during maximal vasodilation were significantly different from those determined with tone intact. These results suggest that although coronary resistance and capacitance are dependent on vasomotor tone, they remain constant throughout diastole and remain similar in the arrested heart.