Six hundred fifty seven patients with angina pectoris underwent coronary angiography after measurement of plasma fibrinogen levels. Coronary artery disease (CAD) was angiographically confirmed in 75% of the patients. Other cardiac disease, either alone or in combination with CAD, was diagnosed in 8% and 11% of cases, respectively; 17% of the patients had no evidence of overt heart disease. Fibrinogen concentrations showed a graded increase according to the severity of coronary stenosis (p = 0.02) but were not significantly associated with any other cardiac heart disease. However, patients with valvular heart diseases had on average a 5.9% elevation of fibrinogen levels as compared to patients without proven cardiac disease (p = 0.08), similar to the observed 6.9% increase for CAD (p = 0.005). On average, patients with cardiomyopathies or pulmonary hypertension had only a 1.6% or 1.2% increase, respectively. The increase in fibrinogen levels associated with CAD was similar in patients with and without coexisting heart diseases. The results demonstrate a significant positive relation of fibrinogen to the presence and severity of CAD irrespective of a possible confounding influence from other cardiac diseases. The results therefore lend support to the hypothesis of a pathogenetic role for fibrinogen as a cardiovascular risk factor.