Heterozygous parents would have the genotype Rr. In a punnett square, this would show a result of 25% homozygous dominant (RR) offspring, 25% homozygous recessive (rr) offspring, and 50% heterozygous (Rr) offspring.
(I attempted to simulate a punnett square with the text)
R r
R| RR | Rr
r | Rr | rr