Chlamydia pneumoniae deoxyribonucleic acid was not found in blood samples (0%) taken from the coronary sinus immediately before coronary angioplasty, but C. pneumoniae deoxyribonucleic acid was detected in 4 of 14 patients' blood samples (29%) taken after coronary angioplasty. This finding suggests that coronary angioplasty can cause C. pneumoniae bacteremia.