Lewis & Short

heus! interj. Used in calling attention, ho! ho there! hark! holloa! heus, reclude: heus, Tranio, etiamne aperis? … heus vos, pueri, quid istic agitis? Plaut. Most. 4, 2, 28 sq.; cf.: Syre, Syre inquam, heus, heus Syre, Ter. Heaut. 2, 3, 107; so, heus, heus, id. Eun. 2, 3, 45; 3, 3, 24; id. Ad. 4, 4, 17: heus, Phaedrome, exi, exi, exi, inquam ocius, Plaut. Curc. 2, 2, 26; cf.: heus, Staphyla, prodi, id. Aul. 2, 6, 1: heus, Strobile, sequere propere me, id. ib. 2, 2, 86: heus, ecquis hic est? holloa there, id. Amph. 4, 1, 12; id. Bacch. 4, 1, 10; id. Most. 4, 2, 19; cf.: heus, ubi estis? id. Capt. 4, 2, 50: heus, audinquid ait? id. ib. 3, 4, 60: et heus, jube illos illinc amabo abscedere, id. Most. 2, 2, 36: heus age, responde, Pers. 2, 17: heus bone, tu palles, id. 3, 94: heus, etiam mensas consumimus? Verg. A. 7, 116: heus tu, te volo, Plaut. Curc. 3, 21; cf. id. ib. 1, 3, 29: heus tu, Rufio, cave sis mentiaris, Cic. Mil. 22, 60: heus tu, Plaut. Curc. 4, 2, 30; 5, 3, 8; id. Cas. 4, 4, 15; Ter. Eun. 1, 2, 22; 3, 5, 46; id. Phorm. 2, 3, 51; Hor. S. 1, 3, 21: heus vos, Plaut. Casin. 2, 2, 2; id. Most. 4, 2, 72; id. Pers. 5, 2, 63: Ch. Atque heus tu. Ni. Quid vis? Plaut. Bacch. 2, 3, 93: Ph. Sed heus tu. Pa. Quid vis? Ter. Eun. 2, 1, 11: sed heus tu, id. ib. 3, 1, 44; id. Heaut. 2, 3, 128; Cic. Att. 1, 16, 13; 15, 11, 4; id. Fam. 7, 11, 2.
Heus always begins a clause, except sometimes in Terence: omnium rerum heus necessitudo est, Ter. Eun. 2, 2, 45.