Three-dimensional distribution of sampled spherical volumes in a mouse heart. The hearts are sampled using volumes with radii of 750 μm. Individual microspheres are represented with the small green spheres. Note that the samples do not include all of the microspheres.

Sampling using individual spheres (as seen in Movie I) yields few flow measurements. Flows can be estimated on refined geometric scale by envisioning a single 750 μm sampling sphere traversing the entire tissue space and recording the number of microspheres in that sphere at each location.

Flow in the mouse heart was measured before and after ligation of a large branch of the left anterior descending artery. Changes in regional flow were evaluated using Poisson statistics.