Managing Your Dog’s Heat Cycle: What Owners Should Know A female dog’s heat cycle is a natural part of her reproductive process. Understanding the different stages — and the emotional and physical changes that come with them — helps you support her calmly and confidently. The Four Stages of the Canine Heat Cycle 1️⃣ Proestrus (Preparation Phase) — 7–10 days The vulva begins to swell Light bleeding usually starts Males show interest, but she is not yet receptive Oestrogen leve