This interrupted case study follows the course of Cara, a high school athlete training for the state championships in cross country. She suffers from polycystic ovarian syndrome and her prescribed medication (spironolactone) greatly diminishes the action of aldosterone on the distal tubule and the collecting duct of kidney nephrons.  During practice her symptoms of dehydration are complicated by her medication with the result that her extracellular levels of sodium and potassium become imbalanced. As Cara's story develops, students will need to learn and explain the mechanism of aldosterone action on the kidney and her symptoms in terms of ion imbalance and membrane depolarization. This case study was written for use in a one-semester animal physiology course, which is taken by junior and senior science majors; it could also be used in an anatomy and physiology course that covers membrane potentials and the role of aldosterone in ion balance and kidney function.