A system for accessing a pericardial cavity and preventing strokes arising from a left atrial appendage, LAA, comprising: a plurality of inflatable balloons including a first inflatable balloon, a second inflatable balloon, and a third inflatable balloon; a catheter having an inner sheath, an outer sheath, and an inner catheter, the inner sheath having a distal end and a proximal end, the first inflatable balloon being attached to the distal end of the inner sheath, the outer sheath having a distal end and a proximal end, the second inflatable balloon being attached to the distal end of the outer sheath, and the inner catheter having a distal end that has a tissue-penetrating tip for puncturing a wall of at least one of the LAA or the pericardial cavity and a proximal end, the third inflatable balloon being attached to the proximal end of the inner catheter; a locking device configured to lock the inner sheath and the outer sheath to render stationary the first inflatable balloon and the second inflatable balloon to seal an ostium of the LAA; an inflation port for inflating at least one inflatable balloon of the first inflatable balloon, the second inflatable balloon, or the third inflatable balloon; a control port for controlling at least one of the inner sheath, the outer sheath, or the inner catheter; and a closure device for sealing the ostium of the LAA and having a suture looped around at least two semi-rigid hollow tubes. a plurality of inflatable balloons including a first inflatable balloon, a second inflatable balloon, and a third inflatable balloon; a catheter having an inner sheath, an outer sheath, and an inner catheter, the inner sheath having a distal end and a proximal end, the first inflatable balloon being attached to the distal end of the inner sheath, the outer sheath having a distal end and a proximal end, the second inflatable balloon being attached to the distal end of the outer sheath, and the inner catheter having a distal end that has a tissue-penetrating tip for puncturing a wall of at least one of the LAA or the pericardial cavity and a proximal end, the third inflatable balloon being attached to the proximal end of the inner catheter; the inner sheath having a distal end and a proximal end, the first inflatable balloon being attached to the distal end of the inner sheath, the outer sheath having a distal end and a proximal end, the second inflatable balloon being attached to the distal end of the outer sheath, and the inner catheter having a distal end that has a tissue-penetrating tip for puncturing a wall of at least one of the LAA or the pericardial cavity and a proximal end, the third inflatable balloon being attached to the proximal end of the inner catheter; a locking device configured to lock the inner sheath and the outer sheath to render stationary the first inflatable balloon and the second inflatable balloon to seal an ostium of the LAA; an inflation port for inflating at least one inflatable balloon of the first inflatable balloon, the second inflatable balloon, or the third inflatable balloon; a control port for controlling at least one of the inner sheath, the outer sheath, or the inner catheter; and a closure device for sealing the ostium of the LAA and having a suture looped around at least two semi-rigid hollow tubes.