Use of heparin to maintain I.V. patency is not recommended (risk of hypotension). Use with caution in previous reactions to sheep products (lanolin). Doses administered as a bolus or in excess of recommendations have been associated with asystole, chest tightness, dyspnea, hypotension, loss of consciousness, and transient tachycardia (infusion over 30 seconds may reduce the potential for these effects). False negative responses may occur in 5% to 10% of patients.