This paper proposes Diffusion-Augmented Contrastive Learning (DACL), a novel hybrid framework that combines diffusion models and supervised contrastive learning for robust representation learning of biosignals. This framework operates on the latent space generated by a lightweight Variational Autoencoder (VAE) trained on Scattering Transformer (ST) features. The forward process of the diffusion model is utilized as a data augmentation technique to generate multiple noisy views of the latent embedding, and a U-Net-style encoder is used to learn noise-robust and class-separable representations at various diffusion time steps using a supervised contrastive learning objective. Experimental results on the PhysioNet 2017 ECG dataset demonstrate an area under the curve (AUROC) of 0.7815.