Complex sentence: Nelson spent the next 25 years at Utah working in the field of cardiothoracic surgery and serving in a variety of LDS Church leadership positions, beginning locally and then as general president of the LDS Church's Sunday School organization from 1971 to 1979.
Split into simpler sentences: Nelson spent the next 25 years at Utah working in the field of cardiothoracic surgery and serving in a variety of LDS Church leadership positions. He served as the general president of the LDS Church's Sunday School organization from 1971 to 1979.