OBJECTIVE: To assess abnormalities in concentrations of cardiac troponin I (cTnI), lactate, and N-terminal pro-B-type natriuretic peptide (NT-proBNP) in relation to arrhythmias, echocardiographic measurements, and survival in dogs with gastric dilatation volvulus (GDV). DESIGN: Prospective observational study. SETTING: University hospital. ANIMALS: Twenty-two dogs with naturally occurring GDV. SAMPLES: Concentrations of cTnI, plasma lactate, and NT-proBNP were recorded at presentation to the emergency room, the time closest to echocardiography, and the highest recorded concentrations during hospitalization. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Cardiac rhythms were categorized on a 0-4 scale (0 = no ventricular premature complexes [VPCs], 1 = single VPCs, 2 = bigeminy or trigeminy, 3 = couplets or triplets, and 4 = R-on-T phenomenon or ventricular tachycardia). Echocardiography was performed 6-18 hours postoperatively. Fifteen dogs had ventricular arrhythmias during hospitalization (Grade 1 [n = 9], Grade 4 [n = 6]). The highest recorded cTnI concentration was significantly higher in the dogs with Grade 4 (P = 0.002) or Grade 1 (P = 0.001) arrhythmias compared to dogs without arrhythmias. Plasma lactate was significantly correlated with left ventricular internal diameter in diastole (r = -0.52, P = 0.01) and systole (r = -0.57, P = 0.006), left ventricular free wall in diastole (LWDd, r = 0.59, P = 0.004), and interventricular septal thickness in diastole (IVDs, r = 0.65, P = 0.001). Dogs that did not survive to 1 week postdischarge (3/22) had a significantly thicker LVWd (P = 0.04) and IVSd (P = 0.05), and received significantly less fluids in the first 24 (P = 0.02) and 48 hours (P = 0.03) of hospitalization. CONCLUSIONS: Concentrations of cTnI and NT-proBNP increased during hospitalization, but only cTnI concentrations were significantly higher in dogs with a higher arrhythmia grade. Additional research on the potential role of serial measurement of biomarkers in dogs with GDV is warranted.