Complex sentence: Against his doctor's advice, Armstrong played a two-week engagement In March 1971 at the Waldorf-Astoria's Empire Room, at the end of which he was hospitalized for a heart attack.
Split into simpler sentences: Against his doctor's advice, Armstrong played a two-week engagement in March 1971 at the Waldorf-Astoria's Empire Room. At the end of it he was hospitalized for a heart attack.