Answer:
He means that in order to introduce American society to the horrible conditions that industrial workers were subjected to and the need for reform, he described the lack of regulations and disgusting occurrences in meat-packing plants. He intended for people to feel sympathetic (heart) but they felt disgusted (stomach).
Step-by-step explanation:
In his novel "The Jungle" Upton Sinclair revealed the disgusting secrets of the meat-packing industry in America and the horrible conditions of its workers.