Both of these stories are similiar, yet different in a way.
For instance, both stories feature couples.In both stories, both wives are caring, loyal, and good. Contrastingly, the husbands do not pay much heed to their wives and are generally uncaring. This leads to the wives playing a part in the deliberately caused deaths of their husbands.And in the end, both wives actually manage to get away with murder.
However, both stories have their differences too. In both stories, the reason the wife has for commiting the murder is different. In LTTS, Mary Maloney kills her husband because she is so attatched to him she simply cannot accept the fact that he is leaving her. However, in The Way Up To Heaven, Mrs Foster murders her husband because she believes that her life will be better without him. Also, in The Way Up To Heaven, Mr Foster is rather dominating, unlike Mr Maloney in Lamb To The Slaughter.