The regional age group event featured as part of the Welsh Athletic Indoor Junior Open.
Heard took the South West title in both the under-15 200m and 300m events.
In the 200m she clocked 26.80 seconds, while in the 300m she ran 42.66 seconds.
Maczugowski, who has recently joined Plymouth, won the South West under-15 shot with a throw of 8.16m in his new age group. He also ran a PB of 28.12 seconds in the 200m and jumped 1.35 in the high jump.
Fern took South West and overall silver in the under-17 girls’ 200m with a time of 26.63 seconds. In the same event, Tavistock’s Grace Wonnacott clocked 29.82 seconds and Plymouth’s Oliver Travers ran 29.94.
Also in the 200m, Plymouth’s Adam Dingley clocked a PB time of 27.89 seconds in the under-15 boys’ 200m, while team-mate Matthew Newton ran 61.79 seconds for the under-17 boys’ 400m and leaped 10.86m in the triple jump.
The next round of the indoor championships will take place on January 5 and will include 60m, 60m hurdles, 800m, 1,500m, pole vault and long jump.