Volunteers are needed for a research study of the effect of exercise while immersed to the neck in water on cardiac (heart) function. Subjects will be instrumented with an intravenous catheter and have their heart and lungs studied with echocardiography, chest x-ray, and magnetic resonance imaging. Prior to the study, subjects must come to the laboratory (about 3 hours) for a physical exam, an exercise test, orientation, and scheduling for the experimental day. The experimental day (2-3 hours) takes place at least three days later. Subjects will be paid $25 for the pre-screen and a total of $150 for completion of the entire study. Subjects must be 18-50 years of age, physically fit (be able to exercise constantly for 40 minutes), and have no physical impairment that would prevent them from participation.For more information, please contact Mike Natoli at firstname.lastname@example.org or 919-668-0017.