  Let E/Q be an elliptic curve and p a rational prime of good ordinary
reduction. For every imaginary quadratic field K/Q satisfying the Heegner
hypothesis for E we have a corresponding line in E(K)\otimes Q_p, known as a
shadow line. When E/Q has analytic rank 2 and E/K has analytic rank 3, shadow
lines are expected to lie in E(Q)\otimes Q_p. If, in addition, p splits in K/Q,
then shadow lines can be determined using the anticyclotomic p-adic height
pairing. We develop an algorithm to compute anticyclotomic p-adic heights which
we then use to provide an algorithm to compute shadow lines. We conclude by
illustrating these algorithms in a collection of examples.
