What are the signs of a blood clot?
Last updated September 3, 2026.
DVT (usually one leg) causes one-sided swelling, pain, warmth, and redness; a pulmonary embolism causes sudden breathlessness, sharp chest pain on deep breaths, racing heart, and sometimes fainting or coughing blood, and that is a 911 call. The one-sided rule is the quickest home check for a leg clot: one calf swollen, warm, tender, and red while the other is normal. Risk context sharpens suspicion: recent surgery or hospitalization, long immobility like flights, estrogen-containing birth control or pregnancy, cancer, obesity, smoking, and any prior clot. The action split is absolute. Suspected DVT: same-day medical evaluation, because the danger is the clot migrating to the lungs, and do not massage or aggressively exercise the leg meanwhile. Suspected PE: sudden breathlessness, sharp pleuritic chest pain, coughing blood, or collapse is emergency-services-now, not an appointment. Caught in time, clots are treated with blood thinners and outcomes are good; the CDC's core message is that these events are often preventable and treatable, with time as the variable that changes everything.
What to do
- One-sided leg swelling, warmth, pain: same-day medical care.
- Sudden breathlessness or sharp chest pain: call 911.
- Know your risk: surgery, long travel, estrogen, cancer, smoking, prior clots.
- Never massage a suspected clot: you do not want it moving.
- Caught early, clots are treatable: blood thinners work.
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