INTRODUCTION/OBJECTIVES: Non-osmotic antidiuretic hormone (ADH) release promotes electrolyte-free water retention in dogs with congestive heart failure (CHF), contributing to low electrolyte concentrations. We hypothesized that dogs with CHF would have higher ADH concentrations than healthy dogs and dogs with preclinical heart disease, and that ADH concentrations would positively correlate to the amount of chloride [Cl ANIMALS, MATERIALS AND METHODS: The study population comprised 20 healthy, 20 preclinical, and 20 CHF dogs. Serum electrolytes, serum osmolality, and plasma ADH were measured and compared between groups using the Kruskal-Wallis test. Relationships between ADH and electrolytes, the amount of [Cl RESULTS: Preclinical (median 6.5 pg/mL
range 1.8 pg/mL-33.8 pg/mL) and CHF (6.7 pg/mL
range 2.0 pg/mL-28.1 pg/mL) dogs had higher ADH concentrations than healthy dogs (median 3.4 pg/mL
range 0.1 pg/mL-6.2 pg/mL) (P=0.004) but there was no difference between preclinical and CHF dogs. Serum ADH was inversely correlated with [Cl DISCUSSION: The inverse relationship between ADH and serum [Cl CONCLUSIONS: Antidiuretic hormone was elevated in dogs with heart disease but was not a unique feature of advanced heart disease.