Background Early dumping and post-bariatric hypoglycemia (PBH) are often addressed as two separate postprandial complications after Roux-en-Y gastric bypass (RYGB). The aim of the study was to evaluate the occurrence of early dumping in RYGB-operated individuals with PBH with and without treatment intervention. Methods Eleven RYGB-operated women with documented PBH each underwent a baseline liquid mixed meal test (MMT) followed by five MMTs preceded by treatment with: acarbose 50 mg for 1 week, sitagliptin 100 mg for 1 week, verapamil 120 mg for 1 week, liraglutide 1.2 mg for 3 weeks, and pasireotide 300 mu g as a single dose. Repetitive venous blood sampling and continuous electrocardiogram recordings were performed at fasting and during a 3-h postprandial period. Results During the baseline MMT, there was a significant increase in HR (from 65 +/- 2 to 90 +/- 4 bpm, p <0.0001) within 30 min after meal intake, while hypoglycemia occurred in the later postprandial period. The HR increase was accompanied by significant increases in serum albumin, plasma norepinephrine, blood glucose, serum insulin, and plasma GLP-1 concentrations. The postprandial HR changes were positively correlated with the changes in insulin and GLP-1 concentrations. Treatment with acarbose and pasireotide both reduced HR, plasma norepinephrine, and serum insulin, and pasireotide also decreased plasma GLP-1. Conclusions RYGB-operated individuals with PBH also have large early postprandial HR increases, hemoconcentration, and sympathetic activation, consistent with early dumping. Moreover, hormone excursions associated with PBH appear to be related to measures of early dumping, suggesting a causal relationship between early dumping and PBH.