A heavy meal diverts blood to the digestive tract, leaving less blood for the heart, said Dr. Larry Sidaway, a cardiologist at Avera St. Luke's Hospital.
"When you eat a meal, a lot of the circulation is diverted to your digestive tract and there's less blood for your heart," he said. "It'd be the same if someone started an exercise program. If they ate a big meal and then went down to exercise on the treadmill, that's not good news."
It is among many things that might increase risk for a heart attack for those shoveling snow.
"If the people have been relatively sedentary and they go out and shovel snow, which is a extremely strenuous activity, (it) puts a lot of stress on the heart and blood circulation," Sidaway said.
The first snowfall of the season often means a spike in the number of people coming in with acute coronary syndrome — commonly called a heart attack, Sidaway said.
"The cold weather causes the arteries to constrict and narrow down," he said. "Then when you go to impose a significant workload on your heart, it's not getting the blood it needs."
For Dr. Samuel Nyamu, a doctor at Sanford Health Aberdeen Clinic, said he's already treated several people who have heart problems from snow shoveling.
On Sunday, a 63-year-old Aberdeen man died of an apparent heart attack while shoveling snow in front of his home. In Mitchell, a 60-year-old Davison County commissioner, formerly of Aberdeen, died of a heart attack.
"I've seen a couple people coming in because of shoveling snow. They just get chest pain or chest discomfort," Nyamu said.
A 2012 study published in "Clinical Research in Cardiology" found 35 of 500 participants experienced a heart attack after shoveling snow. Those who had heart attacks were more likely to be male and have a family history of premature cardiovascular disease.
The typical profile of someone at risk for a heart attack is a man between ages 40 and 70, Sidaway said.
Among the precautions, doctors recommend frequent breaks while shoveling snow.
"You have to do it as your body tells you so. If you're getting tired and getting out of breath, you want to take a break and go back to it later," Nyamu said. "I would say it's quite strenuous, as if you're on a treadmill for four to five miles."
Antoine McGraw, a personal trainer in Aberdeen, said breaks are essential.
"I would definitely take breaks just 'cause it could be too much strain on a person," he said. "Especially if you're not as active before the snow comes."