Contraindications to treatment with DOACs include patients with mechanical heart valves, valvular atrial fibrillation (AF), antiphospholipid syndrome (APLS), concomitant use of drugs that inhibit cytochrome P450-family 3-subfamily A, and P-glycoprotein and patients who are pregnant or breastfeeding. Here, ABCB1 is linked to atrial fibrillation.