Scott Middlemiss crossed the Boston Marathon finish line on Monday with the best sidekick anyone could ask for.

He ran the final few steps with his two-year-old son, Jack, who has Hypertrophic Cardiomyopathy and is waiting for a new heart.

“The first 26 miles were bad yesterday. A lot of aches and pains but the last .2 miles was magical and takes away all the pain,” Scott told CBS Boston.

Scott and his wife, Kate, lost their oldest son, Joseph, to the same condition in 2013 when he was just six years old. Scott ran to honor both of his sons.

After losing Joseph, the family set up the Joseph Middlemiss Big Heart Foundation, which provides the general public with research about congenital heart disease as well as books and other materials to the cardiac floor at Boston Children’s Hospital.