Wearable electrocardiogram (ECG) devices such as smartwatches and ambulatory monitors generate large-scale continuous cardiac data suitable for arrhythmia detection in real-world settings. However, the development of supervised machine learning models is limited by the scarcity of expert-annotated ECG data, class imbalance due to rare arrhythmias, and privacy constraints that restrict data sharing. These challenges make it difficult for traditional deep learning approaches to scale effectively in clinical applications.This work proposes a self-supervised contrastive learning framework that leverages large volumes of unlabeled wearable ECG data to learn meaningful cardiac representations. Using ECG-specific data augmentations, the model is trained to maximize agreement between different views of the same signal while distinguishing between different segments. A deep encoder produces latent embeddings, which are optimized through a contrastive loss, and later adapted for arrhythmia classification using a lightweight classifier with minimal labeled data.The proposed approach reduces dependence on expert annotations, improves generalization across devices and populations, and supports privacy-preserving training. Overall, it offers a scalable and efficient pathway for wearable-based arrhythmia detection, potentially enabling earlier diagnosis and broader deployment of cardiac AI systems in resource-limited healthcare settings.