Savasana is considered both a resting pose and a meditation posture. At the end of an asana class we frequently lie down flat on the floor and use Savasana to reflect on our practice. In pranayama (breath control) practice we generally use support to open the chest.
Almost two years ago my cousin who was in her 30s had congestive heart failure. It was a shock to us all because she didn't have any of the risk factors. To her credit, she made some major changes to her life which included yoga, exercise and nutrition and is now almost fully recovered.
Shortly after the heart failure when she was recovering, on the advice of my dear teacher Victoria Austin, I gave her the following version of Savasana to do twice a day. B.K.S. Iyengar designed what we call either a Simhasana box or a "Heart box" which gives the strongest effect in both opening the upper chest and deeply resting the physical heart at the same time. A fantastic student of mine, Dan Pelsinger, who is a carpenter offered to make the box for us - thank you Dan!
You can create the same shape as the box using two bricks and a bolster or blankets as shown. Both shoulder blades should feel like they are fully supported and the heart should feel like it's almost floating in open space. If you position things right, there should be a deep sense of relaxation but at the same time an experience of lucidity. Like the sun shining in a clear blue sky.