Pulmonary circulation delivers inhaled drugs to left heart first

Steps:

• Drug enters lungs via inhalation and diffuses into pulmonary capillaries.
• This blood, now containing the drug, flows through pulmonary veins.
• Pulmonary veins empty into the left atrium.
• Left atrium receives the drug-laden blood before other chambers.

Why B is correct:

• B (left atrium) is the first chamber post-lungs, per the pathway of pulmonary venous return in standard cardiac anatomy.

Why the others are wrong:

• A (right atrium): Receives deoxygenated blood before lungs, without drug exposure.
• C (left ventricle): Receives blood from left atrium, so second after B.
• D (right ventricle): Pumps blood to lungs, before drug absorption occurs.

Final answer: B