Geometry of the conduit coronary artery in diastole is determined by the volume of the left and right ventricles.

In the canine heart placed in a bath the ramus interventricularis anterior (RIA) was perfused under constant pressure. Segment length and diameter of RIA were monitored by ultrasound technique, coronary pressure by electromanometer. Increasing the volume of the left ventricle by up to 150% of the physiological value increased the segment length by 3.73-12.72% and decreased the diameter by 3.14-9.37%. Similar increments of right ventricular volume increased coronary segment length by 4.38-13.02% and decreased diameter by 2.85-16.45%. In concert with the dynamics of heart deformation segment length and diameter changes were larger in the proximal (close to the basis of the heart) than in the distal part of the artery (close to the apex). Implications of this phenomenon in physiological and/or pathophysiological regulation processes are presented. The results have a methodological implication for in situ studies of coronary smooth muscle activity. When the diameter of the coronary artery is taken as an indicator of smooth muscle activity the ventricular volumes should be kept constant.