Is it a character in the reality it created, or watching from above? Would it even recognize its heartbeats for what they were? Perhaps it would think of these as days in a lifetime.
(For those wondering: the baby is missing all five senses, but can sense the beat of its own heart. There is an interesting idea that if a person was born without any of the senses they would be as good as brain dead because there would be no external stimuli. However, assuming it can still sense the beat of its heart, this might be enough variation – if only in a binary way – to spark thought and imagination. Its whole life would exist around the beat of its heart which it probably wouldn’t even be able to comprehend. Also, since it would be living in a world outside of time as we experience it i.e. no reference point except the heartbeat, it probably could play out a lifetime of its creation in a much shorter span of ‘time’ as we know it)