People with congestive heart failure (CHF) have worse outcomes if their blood chloride concentrations are low, compared to if they are normal. Similarly, low blood chloride concentrations characterize dogs with advanced CHF. Low blood chloride concentrations can be caused by several factors including medications and a failing heart. These concentrations are thought to be more than an indicator of advanced disease, however, and it has been theorized that they contribute to worsening CHF.

Chloride is an electrolyte that is important to the regulation of hormone systems that contribute to the progression of heart disease and heart failure. Insufficient chloride is thought to activate a hormone system called the renin-angiotensin-aldosterone system (RAAS) which contributes to salt and water retention, thus promoting congestion. The relationship between blood chloride and the RAAS has not been explored in any species and this study seeks to determine if blood chloride is inversely related to RAAS hormones that cause salt and water retention. Identifying this relationship would increase understanding of how low blood chloride is related to poor outcomes and could provide a target for treatment. Results from this study have the potential to steer future studies towards finding ways to increase the blood chloride concentrations in dogs with CHF leading to longer and better lives for these dogs.