Several manuscripts have been published describing washout rates of Thallium in men and women. THis is important because Coronary Heart disease affects the rate at which Thallium enters and leaves myocardial cells. Different rates have been described by different authors; some finding men with faster washouts and some with women. We will study 10 men and 10 women normal volunteers with whoe body Thallium scanning after exercise and at preset intervals. Blood samples and a 24 hour urine specimen will be collected. This will allow washout rates to be determined for normal patients and to determine if gender differences are significant and should be considered when Thallium imaging is performed.