Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan. Prepare cake mix according to the package directions. Pour batter into prepared pan.
In a medium bowl, mix together the rhubarb and sugar. Spoon the rhubarb mixture over the cake batter. Drizzle the whipping cream over the top of the rhubarb.
Bake 40 minutes, or until a toothpick inserted into the center of the cake comes out clean. Let cake cool completely before turning it out onto a serving dish.
