We want to know the fundamental mechanisms responsible for regulation of the molecular motors in sarcomeres of heart muscle cells. Our focus is on the molecular switch that turns on the motor. Our major question is: What events signal switch function and how is the switch modulated by sarcomere structure, chemistry, mechanical state and drugs? We approach this question at several levels of organization by integrating information derived from techniques using the disciplines of biophysics, biochemistry as well as molecular, structural and cellular biology. An important clinical objective is the understanding and treatment of acquired and inherited cardiac disorders.