We evaluated the modulation of the viability of immature cardiac myocytes by cardiac fibroblasts after hypothermic preservation using three types of storage solutions—saline, University of Wisconsin solution, and MCDB 107 medium. Cardiac myocytes and fibroblasts were isolated from neonatal rat ventricles, and cultures of myocytes only or co-cultures with fibroblasts (myocyte: fibroblast 2:1) were established. On the fourth day of culture, the cultures were incubated at 4 °C for 6, 12, 18 and 24 hours in the different storage solutions. Enzymes were measured in the storage solutions immediately before and after hypothermic incubation. The cultures were then incubated for an additional 24 hours at 37 °C to evaluate the recovery of the myocyte beating rate. The myocyte beating rate in the co-culture groups showed significantly higher recovery ratios than the corresponding groups in which only myocytes were cultured. Complete recovery was observed in the group co-cultured in MCDB medium 24 hours after hypothermic incubation (83.4% of control—beating rate prior to hypothermic incubation) compared to the other co-cultured groups (15.4, 0%, respectively). Release of enzymes in the co-cultures was significantly suppressed compared to the cultured myocytes, and the greatest suppression was found after 24 hours of incubation in MCDB medium (CPK: 36.6 mIU/flask, LDH: 281.2 mIU/flask) compared to the other two co-cultured groups (CPK: 181.1, 281.1; LDH: 501.7, 773.2). Cardiac fibroblasts diminished myocytic injury after hypothermic preservation using various storage solutions, in which MCDB 107 medium showed the best overall protective effect. Thus, cardiac fibroblasts may play an important role in controlling myocytic viability under various hypothermic conditions.