Complex sentence: Andrei goes to the pool and tries to cross over it but it proves more difficult than he imagined, it remains unclear if the fumes or his poor heart condition or both impede him from achieving his task.
Split into simpler sentences: Andrei goes to the pool and tries to cross over it but it proves more difficult than he imagines. It remains unclear if the fumes, his poor heart condition or both impede him from achieving his task.