Systolic time intervals were studied in 9 patients with documented constrictive pericarditis before and 15 to 20 minutes after intravenous administration of peruvoside (a quick acting digitalis-like glycoside) to determine underlying myocardial dysfunction. Data were compared with those of similarly studied normal subjects and patients with known myocardial dysfunction. Left ventricular ejection time index (LVETI) decreased in normal subjects (P less than 0.01) and in most patients with constrictive pericarditis, and increased marginally in those with myocardial dysfunction (NS) after peruvoside administration. Pre-ejection period index (PEPI) shortened significantly (P less than 0.01) after peruvoside in normal subjects and in patients with myocardial failure, but not in constrictive pericarditis. Likewise the predicted ejection fraction was insignificantly altered in constrictive pericarditis but significantly so (P less than 0.01) in myocardial failure and normal subjects. The response of one patient with constrictive pericarditis to parenteral peruvoside administration was similar to that seen in patients with myocardial failure. This patient had a delayed recovery after pericardiectomy. PEPI/LVETI ratio and ejection fraction were also abnormal in other patients with constrictive pericarditis when compared to normal subjects. Such abnormalities and the unusual response of some patients to administration of peruvoside may reflect underlying myocardial dysfunction in patients with constrictive pericarditis. However, it is possible that the rigid pericardium also contributes to these abnormalities to a varying extent. Systolic time indices and their response to digitalis appear to be a useful, atraumatic method for detecting underlying myocardial dysfunction in patients with constrictive pericarditis.