AbstractCardiovascular malformations were produced in 46.7% of Wistar rats by injecting a sub‐ teratogenic dose of rabbit anti‐rat‐kidney serum and 0.90ml per 100g of rabbit anti‐rat‐heart serum. Ventricular septal defects and aortic arch anomalies were the most common cardiovascular malformations observed. Antikidney serum was found to be very teratogenic, but the 0.10ml per 100g dosage was considered to be sub‐teratogenic. The results suggest that antiheart serum alone is not teratogenic, but when combined with a sub‐teratogenic dose of antikidney serum the combination proved to be teratogenic and resulted in an increase in cardiovascular malformations when compared to the effect of antikidne