To determine whether the changes in blood pressure (BP) which occur following meals in normal people and patients who have substantial falls in BP after a meal postprandial hypotension (PPH)) are associated with changes in cardiac function. Eligible subjects who have been previously diagnosed with PPH will report to the Queen Elizabeth Hospital, on two occasions, following an overnight fast. Subjects will be cannulated and have a BP cuff placed around their upper arm. Following this, subjects will ingest either a drink containing 75 grams of glucose and 150mg of a C13 Acetate (which is metabolised and excreted in the breath, enabling noninvasive measurements of gastric emptying), made up to 300mL water, or on the other study day, 300mL water alone. The order of the study days will be randomised. Following the drink, for 3 hours, measurements will be taken at regular intervals of BP, heart rate, breath samples (on the study day with the Acetate only), blood samples (for measurement of blood glucose and gut hormones) and transthoracic echocardiography (TTE) (for assessment of end systolic and diastolic cardiac volume, cardiac output, cardiac contractility and diastolic function). After the 3 hours of measurements, the cannula will be removed and subjects will be offered lunch prior to leaving the department. Following lunch, on one study day, subjects will have their autonomic nerve function tested noninvasively, using an ECG.