Echoes of a Summer (1976)

Deirdre, age 11, suffers from an incurable heart trouble. For two years, her parents Eugene and Ruth have consulted heart specialists, with no success. Now they have gone to Mahone Bay in Canada, to arrange for her last days to be as pleasant as possible. Philip, the 9-year-old neighbor boy, is the only one who brings a little happiness into the home, because Deirdre knows exactly what's wrong with her. After she suffers from an acute attack and the end comes faster than anybody had thought, Deirdre and Phillip succeed in celebrating her 12th birthday as a day of joy.