Flow patterns within the cardiac ventricles during diastolic filling have been studied in dogs and sheep by cineradiography with fine stream dye injection, and by endoscopic cinephotography. The results show that stable flow patterns occur with little evidence of gross mixing or lateral dispersion. The major flow patterns are expanding vortex systems behind the cusps of the mitral and tricuspid valves. These vortex systems appear important in normal valve dynamics.