| Issue | #40 |
| Published | May-June 1958 |
| Frequency | bi-monthly |
| Cover Price | 0.10 USD |
| Pages | 36 |
| Editing | George T. Delacorte, Jr. (Publisher); Helen Meyer (President); Paul R. Lilly (Executive Vice President); Harold Clark (Vice President-Advertising Director); Albert P. Delacorte (Treasurer) |
| Characters | Lassie |
| Synopsis | Full-page photo of Lassie looking to her left. |
| Genre | adventure; animal; children |
| Pencils | ? (photo) |
| Inks | ? (photo) |
| Colors | ? (photo) |
| Characters | Lassie |
| Synopsis | Full-page introduction to "Heart of a Dog" with black and white photo of Lassie. |
| Genre | adventure; animal; children |
| Pencils | ? (photo) |
| Inks | ? (photo) |
| Letters | typeset |
| Notes | inside front cover |
| Characters | Lassie; Jeff Miller; Ellen Miller (Jeff's mother); Gramps Miller (Jeff's grandfather); Timmy; Porky (Jeff's friend); Pokey (Porky's dog); Ruth Martin; Paul Martin; Doctor |
| Synopsis | Paul and Ruth Martin buy the Miller farm and adopt Timmy. |
| Genre | adventure; animal; children |
| Letters | typeset |
| Notes | story based on a 1957 episode from the CBS television series "Lassie" |
| Characters | Blaze; Calf; Farm Family |
| Synopsis | Blaze saves a calf during a tornado. |
| Genre | adventure; animal; children |
| Letters | typeset |
| Characters | Fuzzy; Dave Adams; Dave's Father; Stray Dog |
| Synopsis | Fuzzy doesn't have pedigree papers but proves he's a champion. |
| Genre | adventure; animal; children |
| Pencils | ? (header illustration) |
| Inks | ? (header illustration) |
| Colors | ? (header illustration) |
| Letters | typeset |
| Characters | Lassie; Timmy; Ruth Martin; Paul Martin; Dash and Star (deer); Zeke Daniffer (poacher); Jeb Daniffer (poacher); Game Warden |
| Synopsis | Poachers threaten Lassie's forest friends. |
| Genre | adventure; animal; children |
| Letters | typeset |