What Causes Pain In Shoulder And Arm After Doing Heavy Physical Activity?

My wife shoveled snow on our driveway. She thinks she overdid it. Several days later, she developed pain from her right shoulder all the way down her arm. She can barely use her right arm and shoulder because of the pain. She's been to her cardiologist. He has ruled out heart problems (she has had a history of substernal chest pain & left arm pain for years). Do you think that even after 3 plus days after the possible overexertion, she could feel such pain, instead right after?