(1) Genetic parameters for the sudden death syndrome (SDS) were estimated in meat-type chickens. Data were collected over 11 generations of selection for body weight within two distinct breeds (Cornish and White Rock). (2) The animal model was used exclusively with linear methods (LM) to estimate genetic parameters. Heritability (h2) of SDS on the liability scale was 0.30 +/- 0.002 and 0.25 +/- 0.002 in the Cornish and White Rock breeds, respectively. (3) A positive genetic correlation (r(g)) with ascites (AS) was determined (approximately 0.3 +/- 0.006). However, it was not possible to estimate the rg of SDS with body weight because of the low prevalence of the defect trait studied (1.8% in the Cornish and 1-5% in the White Rock). (4) Heritability of SDS calculated using male records only was 0.45 +/- 0.009 and 0.35 +/- 0.009, and r(g) with body weight was 0.30 +/- 0.010 and 0.27 +/- 0.009, in the Cornish and White Rock breeds, respectively. (5) In conclusion, the heart defect investigated was heritable with a positive genetic correlation with AS and body weight.