3. Maximal exercise tolerance and peak oxygen consumption: This will be assessed in all patients at baseline and at the end of each 2 month period. Patients will be exercised to exhaustion on a motorized treadmill using a Naughton Protocol. Heart rate and rhythm will be monitored continuously while blood pressure will be measured every 2 minutes. Oxygen consumption, C02 production and respiratory quotient will be calculated every 20 seconds using breath by breath analysis.