A system and method for automatically detecting abnormal heart contractions originating in the ventricles, in a way that is independent of signal morphology is provided. As an uninterrupted series of ventricular detections indicates a possible ventricular arrhythmia, all ventricular beats are detected including isolated premature ventricular contractions (PVCs) and the associated R-R intervals are corrected. Premature ventricular contractions (ectopic beats) in non-standard lead configuration in a noisy signal from an ambulatory subject from a low-cost sensor that may be a small form factor sensor with 1 inch lead separation and may be rotated through multiple placements to correct an R-R interval time series used to detect atrial fibrillation.