it fits = it is great?
Context:
Des Rosiers found that mice given a dose of Viagra –equivalent to the amount a man would receive for erectile dysfunction – coped significantly better than animals not given the drug. Echocardiography and other measures showed that the heart function was better, suggesting that Viagra had protected the heart muscle.
"It makes perfect sense that it would work in these mouse models," says Elizabeth McNally, at the University of Chicago Medical Center, Illinois. "It fits."