Complex sentence: She used Primatene to combat shortness of breath, the epinephrine it contains can cause cardiac arrhythmia, but it was impossible to prove she had taken any just prior to her death.
Split into simpler sentences: She used Primatene to combat shortness of breath. The epinephrine it contains can cause cardiac arrhythmia, but it was impossible to prove she had taken any just prior to her death.