This study will record patient electrocardiograms - as well as various other body signals (e.g., blood pressure, pulse wave, peripheral hemoglobin oxygen saturation) - as monitored routinely both during and immediately subsequent to surgical operations performed under general anesthesia. Through retrospective analysis of patients' heart rate variability (HRV), in concert with the other abovementioned parameters, the investigators seek to forward the development of novel mathematical models and tools for on-line detection of cardiovascular and autonomic dysfunction in the perioperative setting.

Inclusion Criteria:

• Patients undergoing non-cardiac surgery under general anesthesia
• Patients aged 18-80 years
• Patients who are capable of giving informed consent

Exclusion Criteria:

• Patients <18 or >80 years of age
• Patients with an active cardiac pace maker
• Patients with an absent sinus rhythm in ECG
• Patients presenting with a preexisting arrhythmia
• Patients requiring postoperative ICU therapy
• Patients with pheochromocytoma

All patients between the ages of 18 and 80 who are undergoing non-cardiac surgery under general anesthesia at Vienna General Hospital may participate.