If you were miniaturized and injected into someone’s bloodstream, each heartbeat would drag you toward the heart, but the body would recognize you as a danger and signal the white blood cells, which would quickly come over to consume you. If you somehow got past them, you would be forced into the right side of the heart and instantly pumped directly out to the lungs. The vessels would become narrow tubes that slow the flow of blood, which would eventually leave you stuck there.