The Chronic Obstructive Pulmonary Disease Fish Oil (COD-Fish) Pilot Trial will enroll 40-45 participants with COPD. These participants will be randomized to receive Omax3[TM] or placebo (containing corn oil). Omax3[TM] (Cenestra Health) is a 1 gram softgel capsule containing 94.5% omega-3 fatty acids. Each participant will be taking 3 capsules of either Omax3[TM] or matching placebo. The investigators and the subjects will be blinded, meaning that neither the investigators nor the subjects will know if they are taking Omax3[TM] or placebo. All participants will perform a number of noninvasive tests at study entry as well as every two months for a total of six months. They will also undergo pulmonary function testing, flow-mediated dilation (FMD), peripheral arterial tonometry (PAT), six minute-walk tests (6MWT), blood drawing and answer questionnaire data. Thirty participants who agree to it will undergo a separate procedure to collect cells from inside a forearm vein for analysis to be compared to 30 controls. The main purpose of this trial is to examine the effect of Omax3[TM] on endothelial function as measured by change in FMD in patients with COPD. We hypothesize that in subjects with COPD, treatment with Omax3[TM] will increase FMD.