Study to Determine How Cialis Effects the Renal Function in Response to Volume Expansion in Preclinical Systolic Cardiomyopathy (Aim2)

At the consent visit a blood draw will be done also a the 6 minute walk will be done to determine eligibility and a physical exam along with vital signs, height and weight will be done. Twenty-four hour urine collection will be obtained one day prior to the active study day.

Prior to initiation of the study, subjects will be stabilized for at least one week on a no added salt diet (120 milliequivalents of sodium/salt per day (mEq Na/day) which will be maintained throughout the study period.

Subjects will be admitted to the Clinical Research Unit (CRU)on the evening before the active study day. They will be able to order a no-added salt meal and will not have anything to eat after midnight until the last renal clearance blood draw the next day. Bladder scan will be carried out to assess for urine retention. On the active study day, subjects take their medications upon awakening, however, diabetics will hold their diabetic medications until after the last renal clearance test then they will be able to order a regular diet meal and take their diabetic medications. Subjects will be asked to drink 5ml/Kg (milliliters per kilogram of body weight) of water to insure sufficient urinary flow. A priming dose (calculated according to body size) of Iothalamate, to measure glomerular filtration rate (GFR) and para-amino-hippurate (PAH) to measure effective renal plasma flow (ERPF) is infused, followed by a constant rate IV sustaining dose (calculated according to estimated kidney function) of Iothalamate or PAH. The subjects will be asked to empty their bladder spontaneously every thirty minutes. Throughout the study, at the end of each 30-minute clearance period, subjects will be asked to drink an amount of water equivalent to the sum of the blood losses and the urinary flow. After an equilibration period of 45 minutes, a 30-minute baseline renal clearance will be carried out.

Blood pressure will be measured at 20-minute intervals by using automatic blood pressure cuff, and heart rate will be continuously monitored by electrocardiography. Echocardiography will be performed during these baseline clearances to determine left atrial (LA) and Left Ventricular (LV)volumes and systolic and diastolic function.

After the baseline clearance the acute saline load will be administered (normal saline 0.9% 0.25 ml/kg/min for 1 hour). During the 1 hour saline load, one 30-minute clearance (as outlined above) will be repeated with the subjects in supine position after which a second 30-minute clearance will be repeated with the subject sitting or the head of the bed up. As above, blood samples are collected midway during each clearance and urine samples are obtained every 30 minutes. Echocardiography will be repeated immediately after the end of the saline infusion.

At the completion of the baseline renal clearance periods and response to acute sodium load, subjects will be randomized to Tadalafil or placebo. Subjects will be randomized in a 2:1 fashion.

All subjects will take oral Tadalafil (5 mg) or placebo once a day. The blood pressure will be checked prior to administering the drug.Thereafter, both blood pressure and heart rate will continue to be monitored for the next 4 hours. If after the first dose of study drug if patient's systolic blood pressure is \< 85 mmHg systolic and has symptoms of hypotension e.g. lightheadedness, dizziness, feeling faint, blurred vision, the study drug will be stopped however the subject will continue in the study. After 2 hours if blood pressure is >95 systolic then give 1 more (5 mg) of Tadalafil or placebo and monitor blood pressure for 2 hours. If blood pressure is >95 then dismiss subject on 2 (5 mg) tabs of tadalafil or placebo. If blood pressure is between 90 - 95 mmHg systolic, then dismiss on 1 (5 mg) tab of Tadalafil or placebo.

Patients will then be dismissed. Subjects will also have access to a 24-hour phone number should they have any questions or develop any side effects. Subjects will return after one week (+ or - 4 days) for electrolyte check. They will also receive a weekly phone call to review status.

At 2 weeks (± 5 days) from dismissal if blood pressure is> 100 than add 1 (5 mg) tab of Tadalafil or placebo to make a total of 3 (5mg) tabs of Tadalafil or placebo.

At 4 weeks(± 5 days) if blood pressure is > 100 add 1 (5 mg) tab to make a total of 4 (5 mg) Tadalafil or placebo.

After six weeks( + or - 5 days) , subjects will repeat blood draw for safety labs (total blood count and electrolytes). For patients who do not live more than 25 miles away we will try to arrange this visit with the patient's local physician.

At the end of the twelve-week study period (+ or - 8 days), subjects will be admitted to the Clinical Research Unit the afternoon prior to the renal clearance study. Echocardiography, renal clearance, humoral determination and acute saline load will be performed in the same manner as the baseline study. Subjects will also perform a 24-hour urine collection the day prior to their return visit for determination of sodium excretion and creatinine clearance. Subjects will be dismissed after the renal clearance study.