Acute response of pulmonary blood flow and right ventricular function to Dirofilaria immitis adults and microfilaria.

Pulmonary arterial pressures, right ventricular pressures, and right ventricular force of contraction (max dP/dt) were measured before and after the surgical addition of Dirofilaria immitis adults and microfilaria. Six adult anesthetized and heparinized dogs were studied during thoracotomy to compare these pressure measurements with left caudal pulmonary arterial flow. Diversion of pulmonary flow was performed to obtain incremental increases in pulmonary flow through the left caudal lobar artery and to increase right ventricular afterload. The addition of adult heartworm disease, microfilaria, or both did not produce either pulmonary arterial hypertension or increase right ventricular pressure and force of contraction.