Go high or go low? 3C would be NF, 3H would be a splinter, 4C was undiscussed but is presumably better than 3C. If it makes any difference, the 1C bidder might bid a slightly offshape NT here with heart stoppers, so you can presume they are unbalanced or stopperless. It's extremely rare that X isn't 5-7 at this low a level unless responder is perfect t/o shape.
Edit: quick statement clarification in description. Also, this is from an outside source, in case it seems familiar, but I'm interested in what other precision pairs would do in this situation.
1♣-1♥-X-P
2♣-P-?
1♣: 16+ art
X: Usually 5-7, but could be GF if no better bid
2♣: nat 5+ suit, f1rd