Method of reducing left atrial pressure

A method of accessing a vessel, the method comprising:

• providing a first delivery catheter comprising a distal portion having a side outlet opening and a first pre-formed curved distal portion;
• providing a second delivery catheter carrying a medical device, the medical device adapted to be received in a second delivery catheter lumen of the first delivery catheter;
• advancing at least a portion of the first pre-formed curved distal portion into a vessel to position the side outlet opening into the vessel;
• advancing at least a portion of a distal portion of the second delivery catheter out of the first delivery catheter through the side outlet opening;
• and
• piercing a target tissue in the vessel to form an opening in the target tissue using a puncture component associated with a distal end of the second delivery catheter.

A method of accessing a coronary sinus, the method comprising:

• advancing at least a portion of a distal portion of a first delivery catheter into a right atrium, through a coronary sinus ostium, and into the coronary sinus from the right atrium;
• positioning a side outlet opening on the distal portion of the first delivery catheter into the coronary sinus;
• advancing at least a portion of a distal portion of a second delivery catheter out of the first delivery catheter through the side outlet opening, the distal portion of the second delivery catheter carrying an expandable medical device and having a puncture component associated with a distal end of the second delivery catheter;
• and
• deploying the medical device carried on the distal portion of the second delivery catheter to an opening formed in the target tissue;
• wherein the opening extends from a left atrium into the coronary sinus to provide a blood flow pathway, thereby relieving elevated left atrial pressure.