peripheral edema
Peripheral edema is visible swelling of the body's outlying parts — most often the ankles, feet, and lower legs — caused by fluid building up in the tissues. A familiar sign is a sock leaving a deep ring around the ankle, or a finger pressed into the shin leaving a dent that lingers, called pitting. Gravity is why it settles lowest, so it gathers around the ankles in someone who walks and over the lower back in someone confined to bed.
Fluid normally moves out of tiny blood vessels into tissues and back again in a tight balance governed by pressures and proteins. In right-sided or congestive heart failure, blood backs up behind the overloaded heart and venous pressure rises, pushing extra fluid out into the tissues faster than it can return. The body also retains salt and water through hormonal signals, swelling the legs further.
Heart failure is one important cause, but it is far from the only one — leg vein problems, kidney or liver disease, low blood protein, certain medicines, and prolonged sitting can all cause swelling. Whether it is one-sided or both, painful or painless, and accompanied by breathlessness or neck-vein distension helps point toward the underlying reason rather than assuming the heart.
A patient with heart failure notices her shoes feel tight by evening and that pressing her ankle leaves a dent; her weight has crept up three kilograms in a week from retained fluid.
Pitting ankle swelling and a sudden rise in body weight signal fluid retention in heart failure.
Cardiac edema is usually on both legs and painless, whereas one-sided, tender swelling raises concern for a vein clot — a useful but not absolute rule of thumb.