This is the fourth of seven episodes in the Cardiac Physiology Series. Each episode starts with a case where the student finds himself or herself in the imaginary world of a Country Doctor who is called upon to manage a clinical problem related to a 50-minute lecture given by the author to First Year Medical Students. Video tapes of these lectures are divided into short segments which are interwoven with relevant chapters of the author’s text, “The Physiological Basis of Primary Care.”