There's also invisible varicose veins. I get uncomfortably swollen ankles in hot weather. After panicking about my inadequate heart (a slight murmur) my GP reassured me that it's really varicose veins - that with age, the valves in the veins get weaker. In hot weather the vein expands, gets wider, the valves leak a bit and don't manage to push back the blood so efficiently. Putting my legs and feet up for 10 minutes helps bring it down. So far no visible signs, and I hope they stay away cos the NHS wont treat them any more till they get dangerously weak.