OUTLINE: This is a randomized, double blind, multicenter study. Patients are stratified according to those who can complete a 6 minute walking test versus those who cannot. Patients receive either oral theophylline or placebo once daily for 3 days. In the absence of dose limiting toxicity (DLT), patients receive an increased dose for an additional 4 days. In the presence of DLT, patients receive a decreased dose or treatment is stopped. Following completion of the 7 day study period, patients may be given the option to continue on active drug or placebo for 1 additional month unless toxic side effects develop. Quality of life is assessed on days 1 and 8 and at the end of the additional 1 month period.